10-Q

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q

☒ Quarterly report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

for the Quarterly Period Ended March 31, 2021

OR

☐ Transition report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 for the transition period from             to

Commission File Number	Exact name of registrant as specified in its charter; State of Incorporation; Address and Telephone Number	IRS Employer Identification No.
1-14756	Ameren Corporation	43-1723446

(Missouri Corporation)

1901 Chouteau Avenue

St. Louis, Missouri 63103

(314) 621-3222

1-2967 Union Electric Company 43-0559760

(Missouri Corporation)

1901 Chouteau Avenue

St. Louis, Missouri 63103

(314) 621-3222

1-3672 Ameren Illinois Company 37-0211380

(Illinois Corporation)

10 Executive Drive

Collinsville, Illinois 62234

(618) 343-8150

Securities Registered Pursuant to Section 12(b) of the Act:

Title of each class	Trading Symbol(s)	Name of each exchange on which registered
Common Stock, $0.01 par value per share	AEE	New York Stock Exchange

Indicate by check mark whether the registrants: (1) have filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) have been subject to such filing requirements for the past 90 days.

Ameren Corporation	Yes	☒	No	☐
Union Electric Company	Yes	☒	No	☐
Ameren Illinois Company	Yes	☒	No	☐

Indicate by check mark whether each registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).

Ameren Corporation	Yes	☒	No	☐
Union Electric Company	Yes	☒	No	☐
Ameren Illinois Company	Yes	☒	No	☐

Indicate by check mark whether each registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Ameren Corporation	Large accelerated filer	☒	Accelerated filer	☐	Non-accelerated filer	☐
			Smaller reporting company	☐	Emerging growth company	☐
Union Electric Company	Large accelerated filer	☐	Accelerated filer	☐	Non-accelerated filer	☒
			Smaller reporting company	☐	Emerging growth company	☐
Ameren Illinois Company	Large accelerated filer	☐	Accelerated filer	☐	Non-accelerated filer	☒
			Smaller reporting company	☐	Emerging growth company	☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.

Ameren Corporation	☐
Union Electric Company	☐
Ameren Illinois Company	☐

Indicate by check mark whether each registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).

Ameren Corporation	Yes	☐	No	☒
Union Electric Company	Yes	☐	No	☒
Ameren Illinois Company	Yes	☐	No	☒

The number of shares outstanding of each registrant’s classes of common stock as of April 30, 2021, was as follows:

Registrant	Title of each class of common stock	Shares outstanding
Ameren Corporation	Common stock, $0.01 par value per share	255,552,619
Union Electric Company	Common stock, $5 par value per share, held by Ameren Corporation	102,123,834
Ameren Illinois Company	Common stock, no par value, held by Ameren Corporation	25,452,373

______________________________________________________________________________________________________

This combined Form 10-Q is separately filed by Ameren Corporation, Union Electric Company, and Ameren Illinois Company. Each registrant hereto is filing on its own behalf all of the information contained in this quarterly report that relates to such registrant. Each registrant hereto is not filing any information that does not relate to such registrant, and therefore makes no representation as to any such information.

TABLE OF CONTENTS

		Page
Glossary of Terms and Abbreviations		1
Forward-looking Statements		1
PART I. Financial Information
Item 1.	Financial Statements (Unaudited)	4
	Ameren Corporation	4
	Consolidated Statement of Income and Comprehensive Income	4
	Consolidated Balance Sheet	5
	Consolidated Statement of Cash Flows	6
	Consolidated Statement of Shareholders’ Equity	7
	Union Electric Company (d/b/a Ameren Missouri)	8
	Statement of Income (Loss)	8
	Balance Sheet	9
	Statement of Cash Flows	10
	Statement of Shareholders’ Equity	11
	Ameren Illinois Company (d/b/a Ameren Illinois)	12
	Statement of Income	12
	Balance Sheet	13
	Statement of Cash Flows	14
	Statement of Shareholders’ Equity	15
	Note 1. Summary of Significant Accounting Policies	16
	Note 2. Rate and Regulatory Matters	17
	Note 3. Short-term Debt and Liquidity	20
	Note 4. Long-term Debt and Equity Financings	21
	Note 5. Other Income, Net	22
	Note 6. Derivative Financial Instruments	22
	Note 7. Fair Value Measurements	24
	Note 8. Related-party Transactions	26
	Note 9. Commitments and Contingencies	27
	Note 10. Callaway Energy Center	30
	Note 11. Retirement Benefits	31
	Note 12. Income Taxes	32
	Note 13. Supplemental Information	32
	Note 14. Segment Information	35
Item 2.	Management’s Discussion and Analysis of Financial Condition and Results of Operations	37
Item 3.	Quantitative and Qualitative Disclosures About Market Risk	63
Item 4.	Controls and Procedures	63
PART II. Other Information
Item 1.	Legal Proceedings	63
Item 1A.	Risk Factors	64
Item 2.	Unregistered Sales of Equity Securities and Use of Proceeds	64
Item 6.	Exhibits	65
Signatures		66

GLOSSARY OF TERMS AND ABBREVIATIONS

We use the words “our,” “we” or “us” with respect to certain information that relates to Ameren, Ameren Missouri, and Ameren Illinois, collectively. When appropriate, subsidiaries of Ameren Corporation are named specifically as their various business activities are discussed. Refer to the Form 10-K for a complete listing of glossary terms and abbreviations. Only new or significantly changed terms and abbreviations are included below.

Form 10-K – The combined Annual Report on Form 10-K for the year ended December 31, 2020, filed by the Ameren Companies with the SEC.

FORWARD-LOOKING STATEMENTS

Statements in this report not based on historical facts are considered “forward-looking” and, accordingly, involve risks and uncertainties that could cause actual results to differ materially from those discussed. Although such forward-looking statements have been made in good faith and are based on reasonable assumptions, there is no assurance that the expected results will be achieved. These statements include (without limitation) statements as to future expectations, beliefs, plans, projections, strategies, targets, estimates, objectives, events, conditions, and financial performance. In connection with the “safe harbor” provisions of the Private Securities Litigation Reform Act of 1995, we are providing this cautionary statement to identify important factors that could cause actual results to differ materially from those anticipated. The following factors, in addition to those discussed within Risk Factors in the Form 10-K and in this report, and elsewhere in this report and in our other filings with the SEC, could cause actual results to differ materially from management expectations suggested in such forward-looking statements:

•regulatory, judicial, or legislative actions, and any changes in regulatory policies and ratemaking determinations, that may change regulatory recovery mechanisms, such as those that may result from potential future orders and Ameren Missouri’s electric service and natural gas delivery service regulatory rate reviews filed with the MoPSC in March 2021, the July 2020 appeal filed by Ameren Missouri, Ameren Illinois, and ATXI challenging the refund period related to the May 2020 FERC order determining the allowed base ROE under the MISO tariff, the July 2020 appeal filed by Ameren Missouri, Ameren Illinois, and ATXI challenging the FERC’s rehearing denials in the transmission formula rate revision cases, Ameren Illinois’ request for rehearing of the March 2021 FERC order related to Ameren Illinois’ 2020 transmission formula rate update, and Ameren Illinois’ electric distribution service rate reconciliation request filed with the ICC in April 2021;

•the length and severity of the COVID-19 pandemic, and its impacts on our business continuity plans and our results of operations, financial position, and liquidity, including but not limited to changes in customer demand resulting in changes to sales volumes, customers’ payment for our services and their use of deferred payment arrangements, future regulatory or legislative actions that could require suspension of customer disconnections and/or late fees, among other things, for an extended period of time, the health and welfare of our workforce and contractors, supplier disruptions, delays in the completion of construction projects, which could impact our expected capital expenditures and rate base growth, Ameren Missouri’s ability to recover any forgone customer late fee revenues or incremental costs, our ability to meet customer energy-efficiency program goals and earn performance incentives related to those programs, changes in how we operate our business and increased data security risks as a result of the transition to remote working arrangements for a significant portion of our workforce, and our ability to access the capital markets on reasonable terms and when needed;

•the effect and duration of Ameren Illinois’ election to participate in performance-based formula ratemaking framework for its electric distribution service, which, unless extended, expires at the end of 2022, and its participation in electric energy-efficiency programs, including the direct relationship between Ameren Illinois’ ROE and the 30-year United States Treasury bond yields;

•the effect on Ameren Missouri of any customer rate caps pursuant to Ameren Missouri’s election to use the PISA, including an extension of use beyond 2023, if requested by Ameren Missouri and approved by the MoPSC;

•the effects of changes in federal, state, or local laws and other governmental actions, including monetary, fiscal, and energy policies;

•the effects of changes in federal, state, or local tax laws, regulations, interpretations, or rates, and challenges to the tax positions taken by the Ameren Companies, if any, as well as resulting effects on customer rates;

•the effects on energy prices and demand for our services resulting from technological advances, including advances in customer energy efficiency, electric vehicles, electrification of various industries, energy storage, and private generation sources, which generate electricity at the site of consumption and are becoming more cost-competitive;

•the effectiveness of Ameren Missouri’s customer energy-efficiency programs and the related revenues and performance incentives earned under its MEEIA programs;

•Ameren Illinois’ ability to achieve the performance standards applicable to its electric distribution business and the FEJA electric customer energy-efficiency goals and the resulting impact on its allowed ROE;

•our ability to control costs and make substantial investments in our businesses, including our ability to recover costs, investments, and our allowed ROEs within frameworks established by our regulators, while maintaining affordability of our services for our customers;

1

•the cost and availability of fuel, such as low-sulfur coal, natural gas, and enriched uranium used to produce electricity; the cost and availability of purchased power, zero emission credits, renewable energy credits, and natural gas for distribution; and the level and volatility of future market prices for such commodities and credits;

•disruptions in the delivery of fuel, failure of our fuel suppliers to provide adequate quantities or quality of fuel, or lack of adequate inventories of fuel, including nuclear fuel assemblies from the one NRC-licensed supplier of Ameren Missouri’s Callaway Energy Center assemblies;

•the cost and availability of transmission capacity for the energy generated by Ameren Missouri’s energy centers or required to satisfy Ameren Missouri’s energy sales;

•the effectiveness of our risk management strategies and our use of financial and derivative instruments;

•the ability to obtain sufficient insurance, including insurance for Ameren Missouri’s nuclear and coal-fired energy centers, or, in the absence of insurance, the ability to timely recover uninsured losses from our customers;

•the impact of cyberattacks on us or our suppliers, which could, among other things, result in the loss of operational control of energy centers and electric and natural gas transmission and distribution systems and/or the loss of data, such as customer, employee, financial, and operating system information;

•business and economic conditions, which have been affected by, and will be affected by the length and severity of, the COVID-19 pandemic, including the impact of such conditions on interest rates;

•disruptions of the capital markets, deterioration in credit metrics of the Ameren Companies, or other events that may have an adverse effect on the cost or availability of capital, including short-term credit and liquidity;

•the actions of credit rating agencies and the effects of such actions, including any impacts on our credit ratings that may result from the economic conditions of the COVID-19 pandemic;

•the inability of our counterparties to meet their obligations with respect to contracts, credit agreements, and financial instruments, including as it relates to the construction and acquisition of electric and natural gas utility infrastructure and the ability of counterparties to complete projects which is dependent upon the availability of necessary materials and equipment, including those that are affected by the disruptions in the global supply chain caused by the COVID-19 pandemic;

•the impact of weather conditions and other natural phenomena on us and our customers, including the impact of system outages and the level of wind and solar resources;

•the construction, installation, performance, and cost recovery of generation, transmission, and distribution assets;

•the effects of failures of electric generation, electric and natural gas transmission or distribution, or natural gas storage facilities systems and equipment, which could result in unanticipated liabilities or unplanned outages;

•the operation of Ameren Missouri’s Callaway Energy Center, including planned and unplanned outages, such as the current outage that began in December 2020 related to its generator, and the ability to recover costs associated with such outages and the impact of such outages on off-system sales and purchased power, among other things;

•Ameren Missouri’s ability to recover the remaining investment and decommissioning costs associated with the retirement of an energy center, as well as the ability to earn a return on that remaining investment and those decommissioning costs;

•the impact of current environmental laws and new, more stringent, or changing requirements, including those related to NSR and CO2, other emissions and discharges, cooling water intake structures, CCR, and energy efficiency, that could limit or terminate the operation of certain of Ameren Missouri’s energy centers, increase our operating costs or investment requirements, result in an impairment of our assets, cause us to sell our assets, reduce our customers’ demand for electricity or natural gas, or otherwise have a negative financial effect;

•the impact of complying with renewable energy standards in Missouri and Illinois and with the zero emission standard in Illinois;

•Ameren Missouri’s ability to construct and/or acquire wind, solar, and other renewable energy generation facilities, retire energy centers, and implement new or existing customer energy-efficiency programs, including any such construction, acquisition, retirement, or implementation in connection with its Smart Energy Plan, the 2020 IRP, or our emissions reduction goals, and to recover its cost of investment, related return, and, in the case of customer energy-efficiency programs, any lost margins in a timely manner, which is affected by the ability to obtain all necessary regulatory and project approvals, including certificates of convenience and necessity from the MoPSC or any other required approvals for the addition of renewable resources;

•the availability of federal production and investment tax credits related to renewable energy and Ameren Missouri’s ability to use such credits; the cost of wind, solar, and other renewable generation and storage technologies; and our ability to obtain timely interconnection agreements with the MISO or other RTOs at an acceptable cost for each facility;

•advancements in carbon-free generation and storage technologies, and constructive federal and state energy and economic policies with respect to those technologies;

•labor disputes, work force reductions, changes in future wage and employee benefits costs, including those resulting from changes in discount rates, mortality tables, returns on benefit plan assets, and other assumptions;

•the impact of negative opinions of us or our utility services that our customers, investors, legislators, or regulators may have or develop, which could result from a variety of factors, including failures in system reliability, failure to implement our investment plans or to protect sensitive customer information, increases in rates, negative media coverage, or concerns about environmental, social, and/or governance practices;

•the impact of adopting new accounting guidance;

2

•the effects of strategic initiatives, including mergers, acquisitions, and divestitures;

•legal and administrative proceedings; and

•acts of sabotage, war, terrorism, or other intentionally disruptive acts.

New factors emerge from time to time, and it is not possible for management to predict all of such factors, nor can it assess the impact of each such factor on the business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained or implied in any forward-looking statement. Given these uncertainties, undue reliance should not be placed on these forward-looking statements. Except to the extent required by the federal securities laws, we undertake no obligation to update or revise publicly any forward-looking statements to reflect new information or future events.

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PART I. FINANCIAL INFORMATION

ITEM 1. FINANCIAL STATEMENTS.

AMEREN CORPORATION

CONSOLIDATED STATEMENT OF INCOME AND COMPREHENSIVE INCOME

(Unaudited) (In millions, except per share amounts)

	Three Months Ended March 31,
	2021		2020
Operating Revenues:
Electric	$	1,156	$	1,120
Natural gas	410		320
Total operating revenues	1,566		1,440
Operating Expenses:
Fuel	65		140
Purchased power	191		134
Natural gas purchased for resale	165		107
Other operations and maintenance	420		438
Depreciation and amortization	281		255
Taxes other than income taxes	128		125
Total operating expenses	1,250		1,199
Operating Income	316		241
Other Income, Net	46		21
Interest Charges	100		93
Income Before Income Taxes	262		169
Income Taxes	27		21
Net Income	235		148
Less: Net Income Attributable to Noncontrolling Interests	2		2
Net Income Attributable to Ameren Common Shareholders	$	233	$	146
Net Income	$	235	$	148
Other Comprehensive Income, Net of Taxes
Pension and other postretirement benefit plan activity, net of income taxes of $— and $—, respectively	1		1
Comprehensive Income	236		149
Less: Comprehensive Income Attributable to Noncontrolling Interests	2		2
Comprehensive Income Attributable to Ameren Common Shareholders	$	234	$	147
Earnings per Common Share – Basic	$	0.92	$	0.59
Earnings per Common Share – Diluted	$	0.91	$	0.59
Weighted-average Common Shares Outstanding – Basic	254.4		246.4
Weighted-average Common Shares Outstanding – Diluted	255.9		248.1

The accompanying notes are an integral part of these consolidated financial statements.

4

AMEREN CORPORATION

CONSOLIDATED BALANCE SHEET

(Unaudited) (In millions, except per share amounts)

	March 31, 2021		December 31, 2020
ASSETS
Current Assets:
Cash and cash equivalents	$	6	$	139
Accounts receivable – trade (less allowance for doubtful accounts of $47 and $50, respectively)	464		415
Unbilled revenue	210		269
Miscellaneous accounts receivable	61		65
Inventories	467		521
Restricted cash	134		17
Current regulatory assets	367		109
Other current assets	114		118
Total current assets	1,823		1,653
Property, Plant, and Equipment, Net	27,307		26,807
Investments and Other Assets:
Nuclear decommissioning trust fund	1,010		982
Goodwill	411		411
Regulatory assets	1,249		1,100
Other assets	989		1,077
Total investments and other assets	3,659		3,570
TOTAL ASSETS	$	32,789	$	32,030
LIABILITIES AND EQUITY
Current Liabilities:
Current maturities of long-term debt	$	8	$	8
Short-term debt	889		490
Accounts and wages payable	581		958
Taxes accrued	128		82
Interest accrued	84		114
Current regulatory liabilities	225		121
Other current liabilities	392		407
Total current liabilities	2,307		2,180
Long-term Debt, Net	11,527		11,078
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	3,253		3,211
Regulatory liabilities	5,230		5,282
Asset retirement obligations	705		696
Pension and other postretirement benefits	38		37
Other deferred credits and liabilities	452		466
Total deferred credits and other liabilities	9,678		9,692
Commitments and Contingencies (Notes 2, 9, and 10)
Ameren Corporation Shareholders’ Equity:
Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 255.5 and 253.3, respectively	3		3
Other paid-in capital, principally premium on common stock	6,295		6,179
Retained earnings	2,850		2,757
Accumulated other comprehensive loss	—		(1)
Total Ameren Corporation shareholders’ equity	9,148		8,938
Noncontrolling Interests	129		142
Total equity	9,277		9,080
TOTAL LIABILITIES AND EQUITY	$	32,789	$	32,030

The accompanying notes are an integral part of these consolidated financial statements.

5

AMEREN CORPORATION
CONSOLIDATED STATEMENT OF CASH FLOWS
(Unaudited) (In millions)
	Three Months Ended March 31,
	2021		2020
Cash Flows From Operating Activities:
Net income	$	235	$	148
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	295		263
Amortization of nuclear fuel	—		23
Amortization of debt issuance costs and premium/discounts	5		5
Deferred income taxes and investment tax credits, net	26		23
Allowance for equity funds used during construction	(7)		(4)
Stock-based compensation costs	6		6
Other	8		17
Changes in assets and liabilities:
Receivables	(5)		(5)
Inventories	54		23
Accounts and wages payable	(252)		(221)
Taxes accrued	60		47
Regulatory assets and liabilities	(421)		(14)
Assets, other	(9)		(3)
Liabilities, other	(34)		(18)
Pension and other postretirement benefits	4		—
Net cash provided by (used in) operating activities	(35)		290
Cash Flows From Investing Activities:
Capital expenditures	(694)		(636)
Wind generation expenditures	(193)		—
Nuclear fuel expenditures	(1)		(35)
Purchases of securities – nuclear decommissioning trust fund	(152)		(96)
Sales and maturities of securities – nuclear decommissioning trust fund	150		81
Other	1		2
Net cash used in investing activities	(889)		(684)
Cash Flows From Financing Activities:
Dividends on common stock	(140)		(122)
Dividends paid to noncontrolling interest holders	(2)		(2)
Short-term debt, net	399		175
Maturities of long-term debt	—		(85)
Issuances of long-term debt	450		465
Issuances of common stock	125		13
Redemptions of Ameren Illinois preferred stock	(13)		—
Employee payroll taxes related to stock-based compensation	(17)		(20)
Debt issuance costs	(3)		(3)
Other	(4)		—
Net cash provided by financing activities	795		421
Net change in cash, cash equivalents, and restricted cash	(129)		27
Cash, cash equivalents, and restricted cash at beginning of year	301		176
Cash, cash equivalents, and restricted cash at end of period	$	172	$	203

The accompanying notes are an integral part of these consolidated financial statements.

6

AMEREN CORPORATION

CONSOLIDATED STATEMENT OF SHAREHOLDERS’ EQUITY

(Unaudited) (In millions, except per share amounts)

	Three Months Ended March 31,
	2021		2020
Common Stock	$	3	$	2
Other Paid-in Capital:
Beginning of year	6,179		5,694
Settlement of forward sale agreement through common shares issuance	113		—
Shares issued under the DRPlus and 401(k) plan	12		13
Stock-based compensation activity	(9)		(12)
Other paid-in capital, end of period	6,295		5,695
Retained Earnings:
Beginning of year	2,757		2,380
Net income attributable to Ameren common shareholders	233		146
Dividends on common stock	(140)		(122)
Retained earnings, end of period	2,850		2,404
Accumulated Other Comprehensive Income (Loss):
Deferred retirement benefit costs, beginning of year	(1)		(17)
Change in deferred retirement benefit costs	1		1
Deferred retirement benefit costs, end of period	—		(16)
Total accumulated other comprehensive loss, end of period	—		(16)
Total Ameren Corporation Shareholders’ Equity	$	9,148	$	8,085
Noncontrolling Interests:
Beginning of year	142		142
Net income attributable to noncontrolling interest holders	2		2
Dividends paid to noncontrolling interest holders	(2)		(2)
Redemptions of Ameren Illinois preferred stock	(13)		—
Noncontrolling interests, end of period	129		142
Total Equity	$	9,277	$	8,227
Common stock shares outstanding at beginning of year	253.3		246.2
Shares issued under forward sale agreement	1.6		—
Shares issued under the DRPlus and 401(k) plan	0.1		0.2
Shares issued for stock-based compensation	0.5		0.5
Common stock shares outstanding at end of period	255.5		246.9
Dividends per common share	$	0.550	$	0.495

The accompanying notes are an integral part of these consolidated financial statements.

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UNION ELECTRIC COMPANY (d/b/a AMEREN MISSOURI)

STATEMENT OF INCOME (LOSS)

(Unaudited) (In millions)

	Three Months Ended March 31,
	2021		2020
Operating Revenues:
Electric	$	641	$	631
Natural gas	63		49
Total operating revenues	704		680
Operating Expenses:
Fuel	65		140
Purchased power	88		39
Natural gas purchased for resale	31		18
Other operations and maintenance	225		239
Depreciation and amortization	156		139
Taxes other than income taxes	77		79
Total operating expenses	642		654
Operating Income	62		26
Other Income, Net	23		4
Interest Charges	39		40
Income (Loss) Before Income Taxes	46		(10)
Income Tax Benefit	(2)		(1)
Net Income (Loss)	48		(9)
Preferred Stock Dividends	1		1
Net Income (Loss) Available to Common Shareholder	$	47	$	(10)

The accompanying notes as they relate to Ameren Missouri are an integral part of these financial statements.

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UNION ELECTRIC COMPANY (d/b/a AMEREN MISSOURI)

BALANCE SHEET

(Unaudited) (In millions, except per share amounts)

	March 31, 2021		December 31, 2020
ASSETS
Current Assets:
Cash and cash equivalents	$	1	$	136
Advances to money pool	—		139
Accounts receivable – trade (less allowance for doubtful accounts of $15 and $16, respectively)	156		166
Accounts receivable – affiliates	69		57
Unbilled revenue	109		133
Miscellaneous accounts receivable	43		36
Inventories	362		386
Current regulatory assets	141		60
Other current assets	70		79
Total current assets	951		1,192
Property, Plant, and Equipment, Net	14,221		13,879
Investments and Other Assets:
Nuclear decommissioning trust fund	1,010		982
Regulatory assets	413		347
Other assets	375		383
Total investments and other assets	1,798		1,712
TOTAL ASSETS	$	16,970	$	16,783
LIABILITIES AND SHAREHOLDERS’ EQUITY
Current Liabilities:
Current maturities of long-term debt	$	8	$	8
Short-term debt	204		—
Accounts and wages payable	267		501
Accounts payable – affiliates	40		46
Taxes accrued	85		42
Interest accrued	46		53
Current asset retirement obligations	59		60
Other current liabilities	116		123
Total current liabilities	825		833
Long-term Debt, Net	5,096		5,096
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	1,756		1,742
Regulatory liabilities	3,130		3,110
Asset retirement obligations	700		691
Pension and other postretirement benefits	34		35
Other deferred credits and liabilities	59		66
Total deferred credits and other liabilities	5,679		5,644
Commitments and Contingencies (Notes 2, 8, 9, and 10)
Shareholders’ Equity:
Common stock, $5 par value, 150.0 shares authorized – 102.1 shares outstanding	511		511
Other paid-in capital, principally premium on common stock	2,631		2,518
Preferred stock	80		80
Retained earnings	2,148		2,101
Total shareholders’ equity	5,370		5,210
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	$	16,970	$	16,783

The accompanying notes as they relate to Ameren Missouri are an integral part of these financial statements.

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UNION ELECTRIC COMPANY (d/b/a AMEREN MISSOURI)

STATEMENT OF CASH FLOWS

(Unaudited) (In millions)

	Three Months Ended March 31,
	2021		2020
Cash Flows From Operating Activities:
Net income (loss)	$	48	$	(9)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	171		148
Amortization of nuclear fuel	—		23
Amortization of debt issuance costs and premium/discounts	1		2
Deferred income taxes and investment tax credits, net	4		(5)
Allowance for equity funds used during construction	(4)		(2)
Other	3		2
Changes in assets and liabilities:
Receivables	20		(3)
Inventories	24		(18)
Accounts and wages payable	(201)		(172)
Taxes accrued	39		55
Regulatory assets and liabilities	(164)		16
Assets, other	13		2
Liabilities, other	(9)		—
Pension and other postretirement benefits	4		2
Net cash provided by (used in) operating activities	(51)		41
Cash Flows From Investing Activities:
Capital expenditures	(341)		(278)
Wind generation expenditures	(193)		—
Nuclear fuel expenditures	(1)		(35)
Purchases of securities – nuclear decommissioning trust fund	(152)		(96)
Sales and maturities of securities – nuclear decommissioning trust fund	150		81
Money pool advances, net	139		—
Net cash used in investing activities	(398)		(328)
Cash Flows From Financing Activities:
Dividends on preferred stock	(1)		(1)
Short-term debt, net	204		(104)
Maturities of long-term debt	—		(85)
Issuances of long-term debt	—		465
Capital contribution from parent	113		—
Debt issuance costs	—		(3)
Net cash provided by financing activities	316		272
Net change in cash, cash equivalents, and restricted cash	(133)		(15)
Cash, cash equivalents, and restricted cash at beginning of year	145		39
Cash, cash equivalents, and restricted cash at end of period	$	12	$	24

The accompanying notes as they relate to Ameren Missouri are an integral part of these financial statements.

10

UNION ELECTRIC COMPANY (d/b/a AMEREN MISSOURI)

STATEMENT OF SHAREHOLDERS’ EQUITY

(Unaudited) (In millions)

	Three Months Ended March 31,
	2021		2020
Common Stock	$	511	$	511
Other Paid-in Capital:
Beginning of year	2,518		2,027
Capital contribution from parent	113		—
Other paid-in capital, end of period	2,631		2,027
Preferred Stock	80		80
Retained Earnings:
Beginning of year	2,101		1,731
Net income (loss)	48		(9)
Dividends on preferred stock	(1)		(1)
Retained earnings, end of period	2,148		1,721
Total Shareholders’ Equity	$	5,370	$	4,339

The accompanying notes as they relate to Ameren Missouri are an integral part of these financial statements.

11

AMEREN ILLINOIS COMPANY (d/b/a AMEREN ILLINOIS)

STATEMENT OF INCOME

(Unaudited) (In millions)

	Three Months Ended March 31,
	2021		2020
Operating Revenues:
Electric	$	476	$	452
Natural gas	347		271
Total operating revenues	823		723
Operating Expenses:
Purchased power	106		98
Natural gas purchased for resale	134		89
Other operations and maintenance	194		199
Depreciation and amortization	115		107
Taxes other than income taxes	46		42
Total operating expenses	595		535
Operating Income	228		188
Other Income, Net	14		11
Interest Charges	42		39
Income Before Income Taxes	200		160
Income Taxes	50		39
Net Income	150		121
Preferred Stock Dividends	1		1
Net Income Available to Common Shareholder	$	149	$	120

The accompanying notes as they relate to Ameren Illinois are an integral part of these financial statements.

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AMEREN ILLINOIS COMPANY (d/b/a AMEREN ILLINOIS)

BALANCE SHEET

(Unaudited) (In millions)

	March 31, 2021		December 31, 2020
ASSETS
Current Assets:
Cash and cash equivalents	$	—	$	—
Accounts receivable – trade (less allowance for doubtful accounts of $32 and $34, respectively)	293		234
Accounts receivable – affiliates	71		64
Unbilled revenue	101		136
Miscellaneous accounts receivable	5		12
Inventories	105		135
Restricted cash	125		6
Current regulatory assets	217		37
Other current assets	24		23
Total current assets	941		647
Property, Plant, and Equipment, Net	11,358		11,201
Investments and Other Assets:
Goodwill	411		411
Regulatory assets	820		742
Other assets	442		534
Total investments and other assets	1,673		1,687
TOTAL ASSETS	$	13,972	$	13,535
LIABILITIES AND SHAREHOLDERS' EQUITY
Current Liabilities:
Short-term debt	$	323	$	—
Borrowings from money pool	—		19
Accounts and wages payable	255		363
Accounts payable – affiliates	43		51
Customer deposits	70		74
Current regulatory liabilities	200		88
Other current liabilities	207		221
Total current liabilities	1,098		816
Long-term Debt, Net	3,947		3,946
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	1,430		1,367
Regulatory liabilities	1,988		2,063
Pension and other postretirement benefits	67		69
Environmental remediation	51		57
Other deferred credits and liabilities	249		251
Total deferred credits and other liabilities	3,785		3,807
Commitments and Contingencies (Notes 2, 8 and 9)
Shareholders' Equity:
Common stock, no par value, 45.0 shares authorized – 25.5 shares outstanding	—		—
Other paid-in capital	2,692		2,652
Preferred stock	49		62
Retained earnings	2,401		2,252
Total shareholders' equity	5,142		4,966
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$	13,972	$	13,535

The accompanying notes as they relate to Ameren Illinois are an integral part of these financial statements.

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AMEREN ILLINOIS COMPANY (d/b/a AMEREN ILLINOIS)

STATEMENT OF CASH FLOWS

(Unaudited) (In millions)

	Three Months Ended March 31,
	2021		2020
Cash Flows From Operating Activities:
Net income	$	150	$	121
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	115		106
Amortization of debt issuance costs and premium/discounts	3		2
Deferred income taxes and investment tax credits, net	53		22
Other	3		(2)
Changes in assets and liabilities:
Receivables	(24)		(6)
Inventories	30		41
Accounts and wages payable	(40)		(20)
Taxes accrued	3		16
Regulatory assets and liabilities	(255)		(28)
Assets, other	(15)		(4)
Liabilities, other	(9)		(14)
Pension and other postretirement benefits	(1)		(2)
Net cash provided by operating activities	13		232
Cash Flows From Investing Activities:
Capital expenditures	(337)		(324)
Other	—		1
Net cash used in investing activities	(337)		(323)
Cash Flows From Financing Activities:
Dividends on preferred stock	(1)		(1)
Short-term debt, net	323		7
Money pool borrowings, net	(19)		—
Capital contributions from parent	40		100
Redemption of preferred stock	(13)		—
Other	(4)		—
Net cash provided by financing activities	326		106
Net change in cash, cash equivalents, and restricted cash	2		15
Cash, cash equivalents and restricted cash at beginning of year	147		125
Cash, cash equivalents, and restricted cash at end of period	$	149	$	140

The accompanying notes as they relate to Ameren Illinois are an integral part of these financial statements.

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AMEREN ILLINOIS COMPANY (d/b/a AMEREN ILLINOIS)

STATEMENT OF SHAREHOLDERS’ EQUITY

(Unaudited) (In millions)

	Three Months Ended March 31,
	2021		2020
Common Stock	$	—	$	—
Other Paid-in Capital:
Beginning of year	2,652		2,188
Capital contribution from parent	40		100
Other paid-in capital, end of period	2,692		2,288
Preferred Stock:
Beginning of year	62		62
Redemptions of preferred stock	(13)		—
Preferred stock, end of period	49		62
Retained Earnings:
Beginning of year	2,252		1,882
Net income	150		121
Dividends on preferred stock	(1)		(1)
Retained earnings, end of period	2,401		2,002
Total Shareholders’ Equity	$	5,142	$	4,352

The accompanying notes as they relate to Ameren Illinois are an integral part of these financial statements.

15

AMEREN CORPORATION (Consolidated)

UNION ELECTRIC COMPANY (d/b/a Ameren Missouri)

AMEREN ILLINOIS COMPANY (d/b/a Ameren Illinois)

COMBINED NOTES TO FINANCIAL STATEMENTS

(Unaudited)

March 31, 2021

NOTE 1 – SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

General

Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren has other subsidiaries that conduct other activities, such as providing shared services.

•Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri.

•Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois.

•ATXI operates a FERC rate-regulated electric transmission business in the MISO.

The COVID-19 pandemic continues to affect our results of operations, financial position, and liquidity, but we expect a gradual improvement in sales volumes in 2021, compared to 2020. In the first three months of 2021, our sales volumes were comparable to the same period in 2020, excluding the estimated effects of weather and customer energy-efficiency programs. However, we experienced an increase in our accounts receivable balances that were past due or that were a part of a deferred payment arrangement, and a decline in our cash collections from customers. The continued effect of the COVID-19 pandemic on our results of operations, financial position, and liquidity in subsequent periods will depend on its severity and longevity, future regulatory or legislative actions with respect thereto, and the resulting impact on business, economic, and capital market conditions. In general, restrictions on social activities and nonessential businesses implemented in our service territories in 2020 have been relaxed. However, certain restrictions remain in place that limit individual activities and the operation of nonessential businesses and additional restrictions may be imposed in the future.

We continue to assess the impacts the COVID-19 pandemic is having on our businesses, including but not limited to impacts on our liquidity; demand for residential, commercial, and industrial electric and natural gas services; changes in deferred payment arrangements for customers; the timing and extent to which recovery of incremental costs incurred, net of savings, and forgone customer late fee revenues at Ameren Missouri is allowed by the MoPSC; changes in our ability to disconnect customers for nonpayment; bad debt expense; supply chain operations; the availability of our employees and contractors; counterparty credit; capital construction; infrastructure operations and maintenance; energy-efficiency programs; and pension valuations. In March 2021, the MoPSC approved accounting authority orders that allowed Ameren Missouri to accumulate $9 million of certain costs incurred related to the COVID-19 pandemic, net of savings, as well as forgone customer late fees and reconnection fee revenues from March 2020 to March 2021, for potential recovery in the current electric and natural gas service regulatory rate reviews. While the revenues from Ameren Illinois’ electric distribution business, residential and small nonresidential customers of Ameren Illinois’ natural gas distribution business, and Ameren Illinois’ and ATXI’s electric transmission businesses are decoupled from changes in sales volumes, earnings at Ameren Missouri and those associated with Ameren Illinois’ large nonresidential natural gas customers are exposed to such changes. Regarding uncollectible accounts receivable, Ameren Illinois’ electric distribution and natural gas distribution businesses have bad debt riders, which provide for recovery of bad debt write-offs, net of any subsequent recoveries. Ameren Missouri does not have a bad debt rider or tracker, and thus its earnings are exposed to increases in bad debt expense, absent regulatory relief. However, Ameren Missouri does not expect a material impact to earnings from increases in bad debt expense. As of March 31, 2021, accounts receivable balances that were 30 days or greater past due or that were a part of a deferred payment arrangement represented 27%, 19%, and 32%, or $137 million, $33 million, and $104 million, of Ameren’s, Ameren Missouri’s, and Ameren Illinois’ customer trade receivables before allowance for doubtful accounts, respectively. As of March 31, 2020, these percentages were 21%, 16%, and 25%, or $99 million, $29 million, and $70 million, for Ameren, Ameren Missouri, and Ameren Illinois, respectively. For information regarding Ameren Illinois’ suspension and subsequent reinstatement of customer disconnections and late fee charges for nonpayment and Ameren Missouri’s accounting authority orders related to the COVID-19 pandemic, see Note 2 – Rate and Regulatory Matters below.

Ameren’s financial statements are prepared on a consolidated basis and therefore include the accounts of its majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Missouri and Ameren Illinois have no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated.

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Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair statement of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates. The results of operations of an interim period may not give a true indication of results that may be expected for a full year. These financial statements should be read in conjunction with the financial statements and accompanying notes included in the Form 10-K.

Variable Interest Entities

As of March 31, 2021, and December 31, 2020, Ameren had unconsolidated variable interests as a limited partner in various equity method investments, totaling $41 million and $37 million, respectively, included in “Other assets” on Ameren’s consolidated balance sheet. Ameren is not the primary beneficiary of these investments because it does not have the power to direct matters that most significantly affect the activities of these variable interest entities. As of March 31, 2021, the maximum exposure to loss related to these variable interests is limited to the investment in these partnerships of $41 million plus associated outstanding funding commitments of $33 million.

Company-owned Life Insurance

Ameren and Ameren Illinois have company-owned life insurance, which is recorded at the net cash surrender value. The net cash surrender value is the amount that can be realized under the insurance policies at the balance sheet date. As of March 31, 2021, the cash surrender value of company-owned life insurance at Ameren and Ameren Illinois was $275 million (December 31, 2020 – $272 million) and $117 million (December 31, 2020 – $115 million), respectively, while total borrowings against the policies were $107 million (December 31, 2020 – $107 million) at both Ameren and Ameren Illinois. Ameren and Ameren Illinois have the right to offset the borrowings against the cash surrender value of the policies and, consequently, present the net asset in “Other assets” on their respective balance sheets.

NOTE 2 – RATE AND REGULATORY MATTERS

Below is a summary of updates to significant regulatory proceedings and related legal proceedings. See Note 2 – Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K for additional information and a summary of our regulatory frameworks. We are unable to predict the ultimate outcome of these matters, the timing of final decisions of the various agencies and courts, or the impact on our results of operations, financial position, or liquidity.

Missouri

2021 Electric Service Regulatory Rate Review

In March 2021, Ameren Missouri filed a request with the MoPSC seeking approval to increase its annual revenues for electric service by $299 million. The electric rate increase request is based on a 9.9% ROE, a capital structure composed of 51.9% common equity, a rate base of $10.0 billion, and a test year ended December 31, 2020, with certain pro-forma adjustments expected through an anticipated true-up date of September 30, 2021. Ameren Missouri also requested the continued use of the FAC and trackers for pension and postretirement benefits, uncertain income tax positions, and certain excess deferred income taxes that the MoPSC previously authorized in earlier electric rate orders. Additionally, Ameren Missouri requested to recover certain estimated costs associated with the Meramec Energy Center, which is expected to be retired in 2022, over a five-year period. Ameren Missouri requested the use of a tracker for any variances between certain costs collected in customer rates associated with the Meramec Energy Center and actual costs incurred after the date new rates become effective, which would be considered for recovery or refund in a future electric regulatory rate review. The electric rate increase request reflects the following:

•increased infrastructure investments made under Ameren Missouri’s Smart Energy Plan;

•the impact of the transition to a cleaner generation portfolio, including advancing the retirement dates of the Sioux and Rush Island energy centers consistent with Ameren Missouri’s 2020 IRP and 700 MWs of wind generation investment for the High Prairie and Atchison renewable energy centers, which are mitigated by reductions resulting from the request to recover certain Meramec Energy Center costs over a five-year period and the associated tracker;

•decreased weather-normalized customer sales volumes; and

•increased pension and other post-retirement benefits and tax amortization expenses, partially offset by decreased other operations and maintenance expenses.

The MoPSC proceeding relating to the proposed electric service rate changes will take place over a period of up to 11 months, with a decision by the MoPSC expected by February 2022 and new rates effective by March 2022. Ameren Missouri cannot predict the level of any electric service rate change the MoPSC may approve, whether the requested regulatory recovery mechanisms will be approved, or whether

17

any rate change that may eventually be approved will be sufficient for Ameren Missouri to recover its costs and earn a reasonable return on its investments when the rate change goes into effect.

Wind Generation Facility

In January 2021, Ameren Missouri acquired an up-to 300-MW wind generation project located in northwestern Missouri and partially placed it in service as the Atchison Renewable Energy Center. As of the date of this filing, Ameren Missouri has placed approximately half of the project in service, representing a purchase price of approximately $250 million, including an immaterial amount of transaction costs. Ameren Missouri expects the remaining MWs of the project to be in service by the end of September 2021. The Atchison Renewable Energy Center will support Ameren Missouri’s compliance with the Missouri renewable energy standard.

2021 Natural Gas Delivery Service Regulatory Rate Review

In March 2021, Ameren Missouri filed a request with the MoPSC seeking approval to increase its annual revenues for natural gas delivery service by $9 million. The natural gas rate increase request is based on a 9.8% ROE, a capital structure composed of 51.9% common equity, a rate base of $310 million, and a test year ended December 31, 2020, with certain pro-forma adjustments expected through an anticipated true-up date of September 30, 2021. The request includes the continued use of the PGA, ISRS, and DCA and trackers for pension and other postretirement benefits and certain excess deferred taxes that the MoPSC previously authorized in earlier natural gas rate orders.

The MoPSC proceeding relating to the proposed natural gas delivery service rate changes will take place over a period of up to 11 months, with a decision by the MoPSC expected by February 2022 and new rates effective by March 2022. Ameren Missouri cannot predict the level of any natural gas delivery service rate change the MoPSC may approve, or whether any rate change that may eventually be approved will be sufficient for Ameren Missouri to recover its costs and earn a reasonable return on its investments when the rate change goes into effect.

Accounting Authority Orders Related to COVID-19 Pandemic Costs

In March 2021, the MoPSC issued orders approving nonunanimous stipulation and agreements related to Ameren Missouri’s electric and natural gas service accounting authority order requests. The orders allowed Ameren Missouri to accumulate $9 million of certain costs incurred related to the COVID-19 pandemic, net of cost savings, as well as forgone customer late fee and reconnection fee revenues from March 2020 to March 2021, for potential recovery in the electric and natural gas service regulatory rate reviews discussed above. As of March 31, 2021, Ameren Missouri deferred other operations and maintenance expenses of $5 million as a regulatory asset related to the accounting authority orders. If approved for recovery, Ameren Missouri would recognize the remaining $4 million associated with forgone customer late fee and reconnection fee revenue when billed to customers.

Illinois

Electric Distribution Service Rates

In April 2021, Ameren Illinois filed its annual electric distribution service performance-based formula rate update with the ICC, requesting an increase of $64 million in its rates. This update reflects an increase to the annual performance-based formula rate based on 2020 actual costs, an increase to include the 2020 revenue requirement reconciliation adjustment, and an increase for the conclusion of the 2019 revenue requirement reconciliation adjustment, which will be fully refunded to customers in 2021, consistent with the ICC’s December 2020 annual update filing order. It also reflects an increase based on expected net plant additions for 2021. An ICC decision in this proceeding is expected by December 2021, with new rates effective January 2022.

Electric Distribution Service Rate Reconciliation Tariff

In March 2021, the ICC issued an order approving Ameren Illinois’ requested tariff to reconcile its electric distribution service revenue requirement for a period of up to two years after the final customer rate update under performance-based formula ratemaking. To utilize the reconciliation, the ICC-approved tariff requires Ameren Illinois to file a traditional regulatory rate review for its electric distribution service, which may be based on a future test year, by the end of March in the year following the last year in which an annual performance-based formula rate update was permitted. Pursuant to this order, and without legislative change or Ameren Illinois’ election to no longer use performance-based formula ratemaking, Ameren Illinois’ 2022 and 2023 revenues would reflect each year’s actual costs, year-end rate base, and a return at the applicable WACC, with the ROE based on the annual average of the monthly yields of the 30-year United States Treasury bonds plus 580 basis points. The revenue requirement adjustment will be collected from, or refunded to, customers within two years from the end of the reconciled year.

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Electric Energy Efficiency Plan

In March 2021, Ameren Illinois filed with the ICC an energy-efficiency plan which includes annual investments in electric energy-efficiency programs up to approximately $100 million per year from 2022 through 2025. The ICC has the ability to reduce the amount of electric energy-efficiency savings goals in future plan program years if there are insufficient cost-effective programs available, which could reduce the investments in electric energy-efficiency programs. The electric energy-efficiency program investments and the return on those investments are collected from customers through a rider and are not included in the electric distribution service performance-based formula ratemaking framework. A decision by the ICC in this proceeding is expected by September 2021.

QIP Reconciliation Order

In March 2021, the ICC issued an order approving Ameren Illinois’ QIP reconciliation for 2018. The ICC also found that Ameren Illinois’ natural gas capital investments recovered under the QIP during 2018 were accurate and prudent. The ICC order effectively dismissed the Illinois Attorney General’s challenge with respect to 2018 capital investments.

Service Disconnection Moratorium

From March 2020 through March 2021, the ICC limited disconnection activities and late fees for customer nonpayment to varying degrees based on customer class. In March 2021, the ICC issued an order allowing Ameren Illinois to resume disconnection activities for all residential customers through a phased-in approach, which began in April 2021 for customers with the largest past due balances and will resume by June 2021 for all remaining residential customers. The March 2021 order also requires Ameren Illinois to offer deferred payment arrangements, extending to 18 months, to all residential customers through June 2021. In addition, the order requires Ameren Illinois to extend the financial assistance program established by a June 2020 ICC order through 2021. Ameren Illinois is allowed to recover up to $4 million in costs incurred during 2021 related to this financial assistance program. These costs will be deferred as regulatory assets and the portion associated with Ameren Illinois’ electric distribution business will be recovered through its bad debt rider and the portion associated with its natural gas distribution business will be recovered through a special purpose rider.

Federal

Transmission Formula Rate Revisions

In February 2020, the MISO, on behalf of Ameren Missouri, Ameren Illinois, and ATXI, filed requests with the FERC to revise each company’s transmission formula rate calculations with respect to the calculation used for materials and supplies inventories included in rate base. In May 2020, the FERC issued orders approving the revisions prospectively. In addition, the FERC declined to order refunds for earlier periods, as requested by intervenors in Ameren Illinois’ filing, but directed its audit staff to review historical rate recovery in connection with an ongoing FERC audit. In June 2020, Ameren Missouri, Ameren Illinois, and ATXI filed requests for rehearing arguing, among other things, the revisions should be applied retrospectively to include the period January 1, 2019, to June 1, 2020, and that the FERC should not require refunds for periods prior to 2019. In July 2020, the FERC denied the rehearing requests without addressing the issues raised. In July 2020, Ameren Missouri, Ameren Illinois, and ATXI filed an appeal of the July 2020 rehearing denials to the United States Court of Appeals for the District of Columbia Circuit, which is under no deadline to address the appeal. In October 2020, the FERC issued an order reaffirming its May 2020 order and denying the arguments raised in the rehearing requests filed by Ameren Missouri, Ameren Illinois, and ATXI. Regardless of the outcome of the appeal, the impacts of the May 2020 and October 2020 orders are not expected to be material to Ameren’s, Ameren Missouri’s, or Ameren Illinois’ results of operations, financial position, or liquidity.

In March 2021, the FERC issued an order related to an intervenor challenge to Ameren Illinois’ 2020 transmission formula rate update. As a result of this order, in March 2021, Ameren Illinois recorded a regulatory liability of $9 million, largely as a reduction of electric operating revenues, to reflect expected refunds, including interest, primarily related to the historical rate recovery of materials and supplies inventories included in rate base. In April 2021, Ameren Illinois filed a request for rehearing with the FERC regarding its March 2021 order.

FERC Complaint Cases

In November 2013, a customer group filed a complaint case with the FERC seeking a reduction in the allowed base ROE for FERC-regulated transmission rate base under the MISO tariff from 12.38% to 9.15%. In September 2016, the FERC issued an order in the November 2013 complaint case, which lowered the allowed base ROE to 10.32%, or a 10.82% total allowed ROE with the inclusion of a 50 basis point incentive adder for participation in an RTO, that was effective from late September 2016 forward. The September 2016 order also required refunds for the period November 2013 to February 2015, which were paid in 2017. In November 2019, the FERC issued an order addressing the November 2013 complaint case, which set the allowed base ROE at 9.88%, superseding the 10.32% previously ordered, and required refunds, with interest, for the periods November 2013 to February 2015 and from late September 2016 forward. In December 2019, the MISO transmission owners, including Ameren Missouri, Ameren Illinois, and ATXI, filed requests for rehearing with the FERC. In May 2020, the FERC issued an order addressing the requests for rehearing, which set the allowed base ROE at 10.02%, superseding the 9.88%

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previously ordered, and required refunds, with interest, for the periods November 2013 to February 2015 and from late September 2016 forward. In June 2020, various parties filed requests for rehearing with the FERC, challenging the new ROE methodology established by the May 2020 order. In July 2020, the FERC denied the rehearing requests without addressing the issues raised, and indicated it will address the requests for rehearing in a future order. Also in July 2020, Ameren Missouri, Ameren Illinois, and ATXI filed an appeal of the May 2020 order to the United States Court of Appeals for the District of Columbia Circuit challenging the refunds required for the period from September 2016 to May 2020. The court is under no deadline to address the appeal.

As of March 31, 2021, Ameren and Ameren Illinois had recorded current regulatory liabilities of $17 million and $9 million, respectively, to reflect the expected refunds, including interest, associated with the allowed base ROE set by the May 2020 order in the November 2013 complaint case. The increase in the FERC-allowed base ROE resulting from the May 2020 order is not material to Ameren Missouri’s results of operations, financial position, or liquidity.

NOTE 3 – SHORT-TERM DEBT AND LIQUIDITY

The liquidity needs of the Ameren Companies are typically supported through the use of available cash, drawings under committed credit agreements, commercial paper issuances, and, in the case of Ameren Missouri and Ameren Illinois, short-term affiliate borrowings. See Note 4 – Short-term Debt and Liquidity under Part II, Item 8, in the Form 10-K for a description of our indebtedness provisions and other covenants as well as a description of money pool arrangements.

Short-Term Borrowings

The Missouri Credit Agreement and the Illinois Credit Agreement are available to support issuances under Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper programs, respectively, subject to borrowing sublimits, and the issuance of letters of credit. As of March 31, 2021, based on commercial paper outstanding and letters of credit issued under the Credit Agreements, along with cash and cash equivalents, the net liquidity available to Ameren (parent), Ameren Missouri, and Ameren Illinois, collectively, was $1.4 billion. The Ameren Companies were in compliance with the covenants in their Credit Agreements as of March 31, 2021. As of March 31, 2021, the ratios of consolidated indebtedness to consolidated total capitalization, calculated in accordance with the provisions of the Credit Agreements, were 57%, 49%, and 46% for Ameren, Ameren Missouri, and Ameren Illinois, respectively.

The following table presents commercial paper outstanding, net of issuance discounts, as of March 31, 2021, and December 31, 2020. There were no borrowings outstanding under the Credit Agreements as of March 31, 2021, or December 31, 2020.

	March 31, 2021		December 31, 2020
Ameren (parent)	$	362	$	490
Ameren Missouri	204		—
Ameren Illinois	323		—
Ameren consolidated	$	889	$	490

The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances and borrowings under the Credit Agreements in the aggregate for the three months ended March 31, 2021 and 2020:

	Ameren (parent)			Ameren Missouri				Ameren Illinois			Ameren Consolidated
2021
Average daily amount outstanding	$	454		$	99			$	96		$	649
Weighted-average interest rate	0.25		%	0.22		%		0.21		%	0.24		%
Peak amount outstanding during period(a)	$	650		$	206			$	353		$	916
Peak interest rate	0.33		%	0.25		%		0.25		%	0.33		%
2020
Average daily amount outstanding	$	157		$	395			$	76		$	628
Weighted-average interest rate	1.94		%	1.86		%		1.99		%	1.89		%
Peak amount outstanding during period(a)	$	425		$	573			$	150		$	908
Peak interest rate	3.30		%	5.05		%	(b)	3.40		%	5.05		%	(b)

(a)The timing of peak outstanding commercial paper issuances and borrowings under the Credit Agreements varies by company. Therefore, the sum of individual company peak amounts may not equal the Ameren consolidated peak for the period.

(b)Ameren’s and Ameren Missouri’s peak interest rate was affected by temporary disruptions in the commercial paper market in the first quarter of 2020.

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Money Pools

Ameren has money pool agreements with and among its subsidiaries to coordinate and provide for certain short-term cash and working capital requirements. The average interest rate for borrowings under the utility money pool for the three months ended March 31, 2021, was 0.22% (2020 – 1.93%). See Note 8 – Related-party Transactions for the amount of interest income and expense from the utility money pool arrangements recorded by Ameren Missouri and Ameren Illinois for the three months ended March 31, 2021 and 2020.

NOTE 4 – LONG-TERM DEBT AND EQUITY FINANCINGS

Ameren

For the three months ended March 31, 2021, Ameren issued a total of 0.1 million shares of common stock under its DRPlus and 401(k) plan, and received proceeds of $12 million. In addition, in the first quarter of 2021, Ameren issued 0.5 million shares of common stock valued at $33 million upon the vesting of stock-based compensation.

In February 2021, Ameren settled the remainder of the forward sale agreement by physically delivering 1.6 million shares of common stock for cash proceeds of $113 million. The proceeds were used to fund a portion of Ameren Missouri’s wind generation investments. See Note 2 - Rate and Regulatory Matters for additional information about the wind generation investments.

In March 2021, Ameren (parent) issued $450 million of 1.75% senior unsecured notes due March 2028, with interest payable semiannually on March 15 and September 15 of each year, beginning September 15, 2021. Ameren received net proceeds of $447 million, which were used for general corporate purposes, including the repayment of short-term debt.

Ameren Missouri

Ameren Missouri received capital contributions totaling $113 million from Ameren (parent) during the three months ended March 31, 2021.

Ameren Illinois

In March 2021, Ameren Illinois redeemed its 6.625% and 7.75% series preferred stock at par for $12 million and $1 million, respectively. The preferred stock of Ameren Illinois is reflected in “Noncontrolling Interests” on Ameren’s consolidated balance sheet.

Ameren Illinois received capital contributions totaling $40 million from Ameren (parent) during the three months ended March 31, 2021.

Indenture Provisions and Other Covenants

See Note 5 – Long-Term Debt and Equity Financings under Part II, Item 8, in the Form 10-K for a description of our indenture provisions and other covenants, as well as restrictions on the payment of dividends. At March 31, 2021, the Ameren Companies were in compliance with the provisions and covenants contained in their indentures and articles of incorporation, as applicable, and ATXI was in compliance with the provisions and covenants contained in its note purchase agreement.

Off-balance-sheet Arrangements

At March 31, 2021, none of the Ameren Companies had any significant off-balance-sheet financing arrangements, other than variable interest entities. See Note 1 – Summary of Significant Accounting Policies for further detail concerning variable interest entities.

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NOTE 5 – OTHER INCOME, NET

The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the three months ended March 31, 2021 and 2020:

	Three Months
	2021		2020
Ameren:
Allowance for equity funds used during construction	$	7	$	4
Interest income on industrial development revenue bonds	6		6
Other interest income	1		1
Non-service cost components of net periodic benefit income(a)	34		23
Miscellaneous income	4		2
Donations	(3)		(13)		(b)
Miscellaneous expense	(3)		(2)
Total Other Income, Net	$	46	$	21
Ameren Missouri:
Allowance for equity funds used during construction	$	4	$	2
Interest income on industrial development revenue bonds	6		6
Non-service cost components of net periodic benefit income(a)	14		5
Miscellaneous income	1		1
Donations	—		(8)		(b)
Miscellaneous expense	(2)		(2)
Total Other Income, Net	$	23	$	4
Ameren Illinois:
Allowance for equity funds used during construction	$	3	$	2
Interest income	1		1
Non-service cost components of net periodic benefit income	14		13
Miscellaneous income	—		1
Donations	(3)		(4)
Miscellaneous expense	(1)		(2)
Total Other Income, Net	$	14	$	11

(a)For the three months ended March 31, 2021 and 2020, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of less than $(1) million and $6 million, respectively, due to a regulatory tracking mechanism for the difference between the level of such costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates.

(b)Includes $8 million pursuant to Ameren Missouri’s March 2020 electric rate order. See Note 2 – Rate and Regulatory Matters under Part II, Item 8, in the Form 10-K for additional information.

NOTE 6 – DERIVATIVE FINANCIAL INSTRUMENTS

We use derivatives to manage the risk of changes in market prices for natural gas and power, as well as the risk of changes in rail transportation surcharges through fuel oil hedges. Such price fluctuations may cause the following:

•an unrealized appreciation or depreciation of our contracted commitments to purchase or sell when purchase or sale prices under the commitments are compared with current commodity prices;

•market values of natural gas inventories that differ from the cost of those commodities in inventory;

•actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays; and

•actual off-system sales revenues that differ from anticipated revenues

The derivatives that we use to hedge these risks are governed by our risk management policies for forward contracts, futures, options, and swaps. Our net positions are continually assessed within our structured hedging programs to determine whether new or offsetting transactions are required. The goal of the hedging program is generally to mitigate financial risks while ensuring that sufficient volumes are available to meet our requirements. Contracts we enter into as part of our risk management program may be settled financially, settled by physical delivery, or net settled with the counterparty.

All contracts considered to be derivative instruments are required to be recorded on the balance sheet at their fair values, unless the NPNS exception applies. Many of our physical contracts, such as our purchased power contracts, qualify for the NPNS exception to derivative accounting rules. The revenue or expense on NPNS contracts is recognized at the contract price upon physical delivery. The following disclosures exclude NPNS contracts and other non-derivative commodity contracts that are accounted for under the accrual method of accounting.

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If we determine that a contract meets the definition of a derivative and is not eligible for the NPNS exception, we review the contract to determine whether the resulting gains or losses qualify for regulatory deferral. Derivative contracts that qualify for regulatory deferral are recorded at fair value, with changes in fair value recorded as regulatory assets or liabilities in the period in which the change occurs. We believe derivative losses and gains deferred as regulatory assets and liabilities are probable of recovery, or refund, through future rates charged to customers. Regulatory assets and liabilities are amortized to operating income as related losses and gains are reflected in rates charged to customers. Therefore, gains and losses on these derivatives have no effect on operating income. As of March 31, 2021, and December 31, 2020, all contracts that met the definition of a derivative and were not eligible for the NPNS exception received regulatory deferral. Cash flows for all derivative financial instruments are classified in cash flows from operating activities.

The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of March 31, 2021, and December 31, 2020. As of March 31, 2021, these contracts extended through October 2023, October 2026, and May 2032 for fuel oils, natural gas and power, respectively.

	Quantity (in millions, except as indicated)
	March 31, 2021			December 31, 2020
Commodity	Ameren Missouri	Ameren Illinois	Ameren	Ameren Missouri	Ameren Illinois	Ameren
Fuel oils (in gallons)	36	—	36	43	—	43
Natural gas (in mmbtu)	34	114	148	33	114	147
Power (in MWhs)	7	7	14	6	7	13

The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments, as of March 31, 2021, and December 31, 2020:

			March 31, 2021					December 31, 2020
	Balance Sheet Location		Ameren Missouri		Ameren Illinois		Ameren			Ameren Missouri		Ameren Illinois		Ameren
Fuel oils	Other current assets	$	2	$	—	$	2		$	2	$	—	$	2
	Other assets		3		—		3			—		—		—
Natural gas	Other current assets		2		10		12			1		8		9
	Other assets		2		4		6			2		2		4
Power	Other current assets		4		—		4			7		—		7
	Other assets		1		—		1			—		—		—
	Total assets	$	14	$	14	$	28		$	12	$	10	$	22
Fuel oils	Other current liabilities	$	3	$	—	$	3		$	7	$	—	$	7
	Other deferred credits and liabilities		—		—		—			2		—		2
Natural gas	Other current liabilities		—		—		—			1		1		2
	Other deferred credits and liabilities		—		—		—			—		1		1
Power	Other current liabilities		9		16		25			3		17		20
	Other deferred credits and liabilities		5		169		174			8		181		189
	Total liabilities	$	17	$	185	$	202		$	21	$	200	$	221

The Ameren Companies elect to present the fair value amounts of derivative assets and derivative liabilities subject to an enforceable master netting arrangement or similar agreement at the gross amounts on the balance sheet. However, if the gross amounts recognized on the balance sheet were netted with derivative instruments and cash collateral received or posted, the net amounts would not be materially different from the gross amounts at March 31, 2021, and December 31, 2020.

Credit Risk

In determining our concentrations of credit risk related to derivative instruments, we review our individual counterparties and categorize each counterparty into groupings according to the primary business in which each engages. As of March 31, 2021, if counterparty groups were to fail completely to perform on contracts, the Ameren Companies’ maximum exposure related to derivative assets would have been immaterial with or without consideration of the application of master netting arrangements or similar agreements and collateral held.

Certain of our derivative instruments contain collateral provisions tied to the Ameren Companies’ credit ratings. If our credit ratings were downgraded below investment grade, or if a counterparty with reasonable grounds for uncertainty regarding our ability to satisfy an obligation requested adequate assurance of performance, additional collateral postings might be required. The additional collateral required is the net liability position allowed under master netting arrangements or similar agreements, assuming (1) the credit risk-related contingent features underlying these arrangements were triggered and (2) those counterparties with rights to do so requested collateral. As of March 31, 2021, the aggregate fair value of derivative instruments with credit risk-related contingent features in a gross liability position, the cash collateral posted, and the aggregate amount of additional collateral that counterparties could require were each immaterial to Ameren, Ameren

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Missouri, and Ameren Illinois.

NOTE 7 – FAIR VALUE MEASUREMENTS

Fair value is defined as the price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Fair value measurements are classified in three levels based on the fair value hierarchy as defined by GAAP. See Note 8 – Fair Value Measurements under Part II, Item 8, of the Form 10-K for information related to hierarchy levels and valuation techniques.

We consider nonperformance risk in our valuation of derivative instruments by analyzing our own credit standing and the credit standing of our counterparties, and by considering any credit enhancements (e.g., collateral). Included in our valuation, and based on current market conditions, is a valuation adjustment for counterparty default derived from market data such as the price of credit default swaps, bond yields, and credit ratings. No material gains or losses related to valuation adjustments for counterparty default risk were recorded at Ameren, Ameren Missouri, or Ameren Illinois in the three months ended March 31, 2021 or 2020. At March 31, 2021, and December 31, 2020, the counterparty default risk valuation adjustment related to derivative contracts was immaterial for Ameren, Ameren Missouri, and Ameren Illinois.

The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of March 31, 2021, and December 31, 2020:

		March 31, 2021									December 31, 2020
		Level 1		Level 2		Level 3		Total			Level 1		Level 2		Level 3		Total
Assets:
Ameren Missouri
	Derivative assets – commodity contracts:
	Fuel oils	$	4	$	—	$	1	$	5		$	—	$	—	$	2	$	2
	Natural gas	—		4		—		4			—		3		—		3
	Power	2		—		3		5			2		—		5		7
	Total derivative assets – commodity contracts	$	6	$	4	$	4	$	14		$	2	$	3	$	7	$	12
	Nuclear decommissioning trust fund:
	Equity securities:
	U.S. large capitalization	$	679	$	—	$	—	$	679		$	680	$	—	$	—	$	680
	Debt securities:
	U.S. Treasury and agency securities	—		133		—		133			—		115		—		115
	Corporate bonds	—		128		—		128			—		115		—		115
	Other	—		63		—		63			—		67		—		67
	Total nuclear decommissioning trust fund	$	679	$	324	$	—	$	1,003	(a)	$	680	$	297	$	—	$	977	(a)
	Total Ameren Missouri	$	685	$	328	$	4	$	1,017		$	682	$	300	$	7	$	989
Ameren Illinois
	Derivative assets – commodity contracts:
	Natural gas	$	—	$	10	$	4	$	14		$	—	$	6	$	4	$	10
Ameren
	Derivative assets – commodity contracts(b)	$	6	$	14	$	8	$	28		$	2	$	9	$	11	$	22
	Nuclear decommissioning trust fund(c)	679		324		—		1,003		(a)	680		297		—		977		(a)
	Total Ameren	$	685	$	338	$	8	$	1,031		$	682	$	306	$	11	$	999
Liabilities:
Ameren Missouri
	Derivative liabilities – commodity contracts:
	Fuel oils	$	1	$	—	$	2	$	3		$	6	$	—	$	3	$	9
	Natural gas	—		—		—		—			—		1		—		1
	Power	8		—		6		14			8		—		3		11
	Total Ameren Missouri	$	9	$	—	$	8	$	17		$	14	$	1	$	6	$	21
Ameren Illinois
	Derivative liabilities – commodity contracts:
	Natural gas	$	—	$	—	$	—	$	—		$	—	$	1	$	1	$	2
	Power	—		—		185		185			—		—		198		198
	Total Ameren Illinois	$	—	$	—	$	185	$	185		$	—	$	1	$	199	$	200
Ameren
	Derivative liabilities – commodity contracts(b)	$	9	$	—	$	193	$	202		$	14	$	2	$	205	$	221

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(a)Balance excludes $7 million and $5 million of cash and cash equivalents, receivables, payables, and accrued income, net, for March 31, 2021, and December 31, 2020, respectively.

(b)See the Ameren Missouri and Ameren Illinois sections of the table for a breakout of the fair value of Ameren’s derivative assets and liabilities by type of commodity.

(c)See the Ameren Missouri section of the table for a breakout of the fair value of Ameren's nuclear decommissioning trust fund by investment type.

Level 3 fuel oils and natural gas derivative contract assets and liabilities measured at fair value on a recurring basis were immaterial for all periods presented. The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the three months ended March 31, 2021 and 2020:

	2021						2020
	Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois		Ameren
For the three months ended March 31:
Beginning balance at January 1	$	2	$	(198)	$	(196)	$	13	$	(224)	$	(211)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities	(5)		9		4		11		(21)		(10)
Settlements	—		4		4		(7)		4		(3)
Ending balance at March 31	$	(3)	$	(185)	$	(188)	$	17	$	(241)	$	(224)
Change in unrealized gains/(losses) related to assets/liabilities held at March 31	$	(3)	$	9	$	6	$	10	$	(21)	$	(11)

All gains or losses related to our Level 3 derivative commodity contracts are expected to be recovered or returned through customer rates; therefore, there is no impact to either net income or other comprehensive income resulting from changes in the fair value of these instruments.

The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of March 31, 2021, and December 31, 2020:

			Fair Value						Weighted Average(b)
	Commodity		Assets		Liabilities	Valuation Technique(s)	Unobservable Input(a)	Range
2021	Power(c)	$	3	$	(191)	Discounted cash flow	Average forward peak and off-peak pricing – forwards/swaps ($/MWh)	23 – 40	29
							Nodal basis ($/MWh)	(5) – 0	(1)
							Trend rate (%)	2 – 5	3
2020	Power(c)	$	5	$	(201)	Discounted cash flow	Average forward peak and off-peak pricing – forwards/swaps ($/MWh)	23 – 37	29
							Nodal basis ($/MWh)	(6) – 0	(2)
							Trend rate (%)	2 – 6	3

(a)Generally, significant increases (decreases) in these inputs in isolation would result in a significantly higher (lower) fair value measurement.

(b)Unobservable inputs were weighted by relative fair value.

(c)Valuations through 2029 use visible forward prices adjusted for nodal-to-hub basis differentials. Valuations beyond 2029 use a trend rate factor and are similarly adjusted for nodal-to-hub basis differentials.

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The following table sets forth the carrying amount and, by level within the fair value hierarchy, the fair value of financial assets and liabilities disclosed, but not recorded, at fair value as of March 31, 2021, and December 31, 2020:

	Carrying Amount			Fair Value
				Level 1		Level 2		Level 3			Total
	March 31, 2021
Ameren:
Cash, cash equivalents, and restricted cash	$	172		$	172	$	—	$	—		$	172
Investments in industrial development revenue bonds(a)	256			—		256		—			256
Short-term debt	889			—		889		—			889
Long-term debt (including current portion)(a)	11,535		(b)	—		12,233		507		(c)	12,740
Ameren Missouri:
Cash, cash equivalents, and restricted cash	$	12		$	12	$	—	$	—		$	12
Investments in industrial development revenue bonds(a)	256			—		256		—			256
Short-term debt	204			—		204		—			204
Long-term debt (including current portion)(a)	5,104		(b)	—		5,685		—			5,685
Ameren Illinois:
Cash, cash equivalents, and restricted cash	$	149		$	149	$	—	$	—		$	149
Short-term debt	323			—		323		—			323
Long-term debt (including current portion)	3,947		(b)	—		4,401		—			4,401
	December 31, 2020
Ameren:
Cash, cash equivalents, and restricted cash	$	301		$	301	$	—	$	—		$	301
Investments in industrial development revenue bonds(a)	256			—		256		—			256
Short-term debt	490			—		490		—			490
Long-term debt (including current portion)(a)	11,086		(b)	—		12,778		537		(c)	13,315
Ameren Missouri:
Cash, cash equivalents, and restricted cash	$	145		$	145	$	—	$	—		$	145
Advances to money pool	139			—		139		—			139
Investments in industrial development revenue bonds(a)	256			—		256		—			256
Long-term debt (including current portion)(a)	5,104		(b)	—		6,160		—			6,160
Ameren Illinois:
Cash, cash equivalents, and restricted cash	$	147		$	147	$	—	$	—		$	147
Borrowings from money pool	19			—		19		—			19
Long-term debt (including current portion)	3,946		(b)	—		4,822		—			4,822

(a)Ameren and Ameren Missouri have investments in industrial development revenue bonds, classified as held-to-maturity and recorded in “Other Assets,” that are equal to the finance obligations for the Peno Creek and Audrain CT energy centers. As of March 31, 2021, and December 31, 2020, the carrying amount of both the investments in industrial development revenue bonds and the finance obligations approximated fair value.

(b)Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $86 million, $36 million, and $36 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of March 31, 2021. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $84 million, $36 million, and $36 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2020.

(c)The Level 3 fair value amount consists of ATXI’s senior unsecured notes.

NOTE 8 – RELATED-PARTY TRANSACTIONS

In the ordinary course of business, Ameren Missouri and Ameren Illinois have engaged in, and may in the future engage in, affiliate transactions. These transactions primarily consist of natural gas and power purchases and sales, services received or rendered, and borrowings and lendings. Transactions between Ameren’s subsidiaries are reported as affiliate transactions on their individual financial statements, but those transactions are eliminated in consolidation for Ameren’s consolidated financial statements. For a discussion of material related-party agreements and money pool arrangements, see Note 13 – Related-party Transactions and Note 4 – Short-term Debt and Liquidity under Part II, Item 8, of the Form 10-K. For information Ameren Missouri’s and Ameren Illinois’ capital contributions, see Note 4 – Long-term Debt and Equity Financings.

Electric Power Supply Agreement

In April 2021, Ameren Illinois conducted a procurement event, administered by the IPA, to purchase energy products. Ameren Missouri was among the winning suppliers in this event. As a result, in April 2021, Ameren Missouri and Ameren Illinois entered into an energy product agreement by which Ameren Missouri agreed to sell and Ameren Illinois agreed to purchase, 33,600 MWhs at an average price of $34 per MWh during the period of July 2022 through November 2022.

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Tax Allocation Agreement

See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of the Form 10-K for a discussion of the tax allocation agreement. The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of March 31, 2021, and December 31, 2020:

	March 31, 2021				December 31, 2020
	Ameren Missouri		Ameren Illinois		Ameren Missouri		Ameren Illinois
Income taxes payable to parent(a)	$	—	$	6	$	—	$	6
Income taxes receivable from parent(b)	14		18		9		15

(a)Included in “Accounts payable – affiliates” on the balance sheet.

(b)Included in “Accounts receivable – affiliates” on the balance sheet.

Effects of Related-party Transactions on the Statement of Income

The following table presents the effect on Ameren Missouri and Ameren Illinois of related-party transactions for the three months ended March 31, 2021 and 2020:

				Three Months
Agreement	Income Statement Line Item			Ameren Missouri		Ameren Illinois
Ameren Missouri power supply	Operating Revenues	2021	$	2	$	(a)
agreements with Ameren Illinois		2020		3		(a)
Ameren Missouri and Ameren Illinois	Operating Revenues	2021	$	7	$	(b)
rent and facility services		2020		7		1
Ameren Missouri and Ameren Illinois miscellaneous	Operating Revenues	2021	$	(b)	$	(b)
support services and services provided to ATXI		2020		(b)		(b)
Total Operating Revenues		2021	$	9	$	(b)
		2020		10		1
Ameren Illinois power supply	Purchased Power	2021	$	(a)	$	2
agreements with Ameren Missouri		2020		(a)		3
Ameren Missouri and Ameren Illinois	Purchased Power	2021	$	1	$	(b)
transmission services from ATXI		2020		(a)		(b)
Total Purchased Power		2021	$	1	$	2
		2020		(a)		3
Ameren Missouri and Ameren Illinois	Other Operations and Maintenance	2021	$	(b)	$	1
rent and facility services		2020		(b)		1
Ameren Services support services	Other Operations and Maintenance	2021	$	35	$	33
agreement		2020		35		33
Total Other Operations and		2021	$	35	$	34
Maintenance		2020		35		34
Money pool borrowings (advances)	(Interest Charges)/Other Income, Net	2021	$	(b)	$	(b)
		2020		(b)		(b)

(a)Not applicable.

(b)Amount less than $1 million.

NOTE 9 – COMMITMENTS AND CONTINGENCIES

We are involved in legal, tax, and regulatory proceedings before various courts, regulatory commissions, authorities, and governmental agencies with respect to matters that arise in the ordinary course of business, some of which involve substantial amounts of money. We believe that the final disposition of these proceedings, except as otherwise disclosed in the notes to our financial statements in this report and in the Form 10-K, will not have a material adverse effect on our results of operations, financial position, or liquidity.

Reference is made to Note 1 – Summary of Significant Accounting Policies, Note 2 – Rate and Regulatory Matters, Note 9 – Callaway Energy Center, Note 13 – Related-party Transactions, and Note 14 – Commitments and Contingencies under Part II, Item 8, of the Form 10-K. See also Note 1 – Summary of Significant Accounting Policies, Note 2 – Rate and Regulatory Matters, Note 8 – Related-party Transactions, and Note 10 – Callaway Energy Center of this report.

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Environmental Matters

Our electric and gas generation, transmission, distribution and gas storage operations must comply with a variety of environmental statutory and regulatory requirements, including permitting programs implemented via federal, state, and local authorities. Depending upon the specific business activity of the facility, such laws address air emissions; discharges to water bodies; the storage, handling, and disposal of hazardous substances and waste materials; siting and land use requirements; and potential ecological impacts. Complex and lengthy processes are required to obtain and renew approvals, permits, and licenses for new, existing, or modified facilities. Additionally, the use and handling of various chemicals or hazardous materials require release prevention plans and emergency response procedures. We employ dedicated personnel knowledgeable in environmental matters to oversee our business activities’ compliance with regulatory requirements.

Environmental regulations have a significant impact on the electric utility industry and compliance with these regulations could be costly for Ameren Missouri, which operates coal-fired power plants. Clean Air Act regulations that apply to the electric utility industry include the NSPS, the CSAPR, the MATS, and the National Ambient Air Quality Standards, which are subject to periodic review for certain pollutants. Collectively, these regulations cover a variety of pollutants, such as SO2, particulate matter, NOx, mercury, toxic metals, and acid gases, and CO2 emissions from new power plants. Clean Water Act regulations applicable to coal-fired power plants govern both intake and discharges of water and require evaluation of the ecological and biological impact of our operations and could require modifications to water intake structures or more stringent limitations on wastewater discharges. Depending upon the scope of modifications ultimately required by state regulators, these capital expenditures could be significant. The management and disposal of coal ash is regulated under the Resource Conservation and Recovery Act and the CCR rule and requires the closure of our surface impoundments at Ameren Missouri’s coal-fired energy centers. The individual or combined effects of existing and new environmental regulations could result in significant capital expenditures, increased operating costs, or the closure or alteration of operations at some of Ameren Missouri’s energy centers. Ameren and Ameren Missouri expect that such compliance costs would be recoverable through rates, subject to MoPSC prudence review, but the timing of costs and their recovery could be subject to regulatory lag.

Ameren and Ameren Missouri estimate that they will need to make capital expenditures of $175 million to $225 million from 2021 through 2025 in order to comply with existing environmental regulations. Additional environmental controls beyond 2025 could be required. This estimate of capital expenditures includes ash pond closure and corrective action measures required by the CCR regulations, potential modifications to cooling water intake structures at existing power plants under Clean Water Act rules, and by effluent limitation guidelines applicable to steam electric generating units, all of which are discussed below. This estimate does not include capital expenditures that may be required as a result of the NSR and Clean Air Act litigation discussed below. Ameren Missouri’s current plan for compliance with existing air emission regulations includes burning low-sulfur coal and installing new or optimizing existing air pollution control equipment. The actual amount of capital expenditures required to comply with existing environmental regulations may vary substantially from the above estimates because of uncertainty as to future permitting requirements made by state regulators and the EPA, potential revisions to regulatory obligations, and the cost of potential compliance strategies, among other things.

The following sections describe the more significant environmental laws and rules and environmental enforcement and remediation matters that affect or could affect our operations. The EPA has initiated an administrative review of several regulations and proposed amendments to regulations and guidelines, including to the effluent limitation guidelines and the CCR Rule, which could ultimately result in the revision of all or part of such rules.

Clean Air Act

Federal and state laws, including CSAPR, regulate emissions of SO2 and NOx through the reduction of emissions at their source and the use and retirement of emission allowances. CSAPR is implemented through a series of phases, and the second phase became effective in 2017. Additional emission reduction requirements may apply in subsequent years. Ameren Missouri complies with current CSAPR requirements by minimizing emissions through the use of low-sulfur coal, operation of two scrubbers at its Sioux Energy Center, and optimization of other existing air pollution control equipment. Ameren Missouri could incur additional costs to lower its emissions at one or more of its energy centers to comply additional CSAPR requirements in future years. These additional costs for compliance are expected to be recovered from customers through the FAC or higher base rates.

CO2 Emissions Standards

The EPA’s Affordable Clean Energy Rule repealed the Clean Power Plan and replaced it with a new rule that established emission guidelines for states to follow in developing plans to limit CO2 emissions and identified certain efficiency measures as the best system of emission reduction for coal-fired electric generating units. In January 2021, the United States Court of Appeals for the District of Columbia Circuit vacated the Affordable Clean Energy Rule, and ruled that the EPA had the discretion to consider emission reduction measures that include efficiency measures and generation shifting to lower carbon emissions. The United States Supreme Court has extended the deadline for seeking review, and a decision on whether the Supreme Court will review the circuit court's ruling could occur in fall 2021. Regardless of the outcome of those legal challenges, the EPA is likely to develop new regulations to address carbon emissions from coal and natural gas electric generating units. At this time, Ameren Missouri cannot predict the outcome of legal challenges to the vacated Affordable Clean

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Energy Rule or future rulemakings. As such, the impact on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri is uncertain.

NSR and Clean Air Litigation

In January 2011, the Department of Justice, on behalf of the EPA, filed a complaint against Ameren Missouri in the United States District Court for the Eastern District of Missouri alleging that in performing projects at its coal-fired Rush Island Energy Center in 2007 and 2010, Ameren Missouri violated provisions of the Clean Air Act and Missouri law. In January 2017, the district court issued a liability ruling and, in September 2019, entered a final order that required Ameren Missouri to install a flue gas desulfurization system at the Rush Island Energy Center and a dry sorbent injection system at the Labadie Energy Center. There were no fines in the order as the Department of Justice previously dismissed claims for penalties. The district court stayed implementation of the majority of the requirements of its order while the case is under appeal to the United States Court of Appeals for the Eighth Circuit. In December 2020, the court of appeals heard oral arguments presented by the parties. The court is under no deadline to issue a ruling in this case and Ameren Missouri is unable to predict the ultimate resolution of this matter. Ameren Missouri expects a ruling by the court of appeals during 2021.

The ultimate resolution of this matter could have a material adverse effect on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri. Among other things and subject to economic and regulatory considerations, resolution of this matter could result in increased capital expenditures for the installation of air pollution control equipment, as well as increased operations and maintenance expenses. Based upon engineering studies from October 2019, capital expenditures to comply with the district court’s order for installation of a flue gas desulfurization system at the Rush Island Energy Center are estimated at approximately $1 billion. Further, the flue gas desulfurization system would result in additional operation and maintenance expenses of $30 million to $50 million annually for the life of the energy center. Engineering studies required to develop estimated capital expenditures and estimated additional operation and maintenance expenses for the Labadie Energy Center to comply with the district court’s order will not be undertaken while the case is under appeal. As a result of the district court’s stay, Ameren Missouri does not expect to make significant capital expenditures or incur operations and maintenance expenses related to the district court’s order while the case is under appeal.

Clean Water Act

The EPA’s Section 316(b) Rule requires power plant operators to evaluate cooling water intake structures and identify measures for reducing the number of aquatic organisms impinged on a power plant’s cooling water intake screens or entrained through the plant’s cooling water system. All of Ameren Missouri’s coal-fired and nuclear energy centers are subject to the cooling water intake structures rule. Requirements of the rule are implemented by state regulators through the permit renewal process of each energy center’s water discharge permit, which is expected to be completed by 2023.

In 2015, the EPA issued a rule to revise the effluent limitation guidelines applicable to steam electric generating units. These guidelines established national standards for water discharges, prohibits effluent discharges of certain waste streams, and imposes more stringent limitations on certain water discharges from power plants. To meet the requirements of the guidelines, Ameren Missouri installed dry ash handling systems and in 2020 completed construction of wastewater treatment facilities at three of its four coal-fired energy centers. The Meramec Energy Center is scheduled to close permanently in 2022, and as a result, does not require new wastewater and dry ash handling systems. Estimated capital expenditures to complete these projects are included in the CCR management compliance plan, discussed below.

CCR Management

The EPA’s CCR rule establishes requirements for the management and disposal of CCR from coal-fired power plants and will result in the closure of surface impoundments at Ameren Missouri’s energy centers. Ameren Missouri is in the process of closing surface impoundments at all of its facilities, and is scheduled to complete the last of such closures in 2023. The EPA has issued a series of revisions to the CCR rule; however, none of those revisions is expected to materially impact our closure schedule. Ameren and Ameren Missouri have AROs of $103 million recorded on their respective balance sheets as of March 31, 2021, associated with CCR storage facilities. Ameren Missouri estimates it will need to make capital expenditures of $75 million to $100 million from 2021 through 2025 to implement its CCR management compliance plan, which includes installation of groundwater monitoring equipment and water treatment facilities.

Remediation

The Ameren Companies are involved in a number of remediation actions to clean up sites impacted by the use or disposal of materials containing hazardous substances. Federal and state laws can require responsible parties to fund remediation regardless of their degree of fault, the legality of original disposal, or the ownership of a disposal site.

As of March 31, 2021, Ameren Illinois has remediated the majority of the 44 former MGP sites in Illinois and could substantially conclude remediation efforts at the remaining sites by 2023. The ICC allows Ameren Illinois to recover such remediation and related litigation costs from its electric and natural gas utility customers through environmental cost riders that are subject to annual prudence review by the ICC. As

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of March 31, 2021, Ameren Illinois estimated the remaining obligation related to these former MGP sites at $90 million to $150 million. Ameren and Ameren Illinois recorded a liability of $90 million to represent the estimated minimum obligation for these sites, as no other amount within the range was a better estimate.

The scope of the remediation activities at these former MGP sites may increase as remediation efforts continue. Considerable uncertainty remains in these estimates because many site-specific factors can influence the ultimate actual costs, including unanticipated underground structures, the degree to which groundwater is encountered, regulatory changes, local ordinances, and site accessibility. The actual costs and timing of completion may vary substantially from these estimates.

Our operations or those of our predecessor companies involve the use of, disposal of, and, in appropriate circumstances, the cleanup of substances regulated under environmental laws. We are unable to determine whether such historical practices will result in future environmental commitments or will affect our results of operations, financial position, or liquidity.

NOTE 10 – CALLAWAY ENERGY CENTER

See Note 9 – Callaway Energy Center under Part II, Item 8, of the Form 10-K for information regarding spent nuclear fuel recovery, recovery of decommissioning costs, and the nuclear decommissioning trust fund. The fair value of the trust fund for Ameren Missouri’s Callaway Energy Center is reported as “Nuclear decommissioning trust fund” in Ameren’s and Ameren Missouri’s balance sheets. This amount is legally restricted and may be used only to fund the costs of nuclear decommissioning. Changes in the fair value of the trust fund are recorded as an increase or decrease to the nuclear decommissioning trust fund, with an offsetting adjustment to the related regulatory liability. Ameren and Ameren Missouri have recorded an ARO for the Callaway Energy Center decommissioning costs at fair value, which represents the present value of estimated future cash outflows. Annual decommissioning costs of $7 million are included in the costs used to establish electric rates for Ameren Missouri’s customers. Every three years, the MoPSC requires Ameren Missouri to file an updated cost study and funding analysis for decommissioning its Callaway Energy Center. An updated cost study and funding analysis was filed with the MoPSC in November 2020 and reflected within the ARO. In February 2021, the MoPSC approved no change in electric rates for decommissioning costs based on Ameren Missouri’s updated cost study funding analysis. See Note 13 – Supplemental Information for more information on Ameren Missouri’s AROs.

Maintenance Outage

During its return to full power after the completion of the last refueling and maintenance outage in late December 2020, the Callaway Energy Center experienced a non-nuclear operating issue related to its generator. A thorough investigation of this matter was conducted. Work continues to replace certain key components of the generator in order to return the energy center to service. Ameren Missouri expects generator repairs of approximately $65 million, which are expected to be largely capital expenditures. Due to the long lead time for the manufacture, repair, and installation of the components, the energy center is expected to return to service in July 2021. In April 2021, Ameren Missouri’s insurance claims were accepted by NEIL, which are expected to cover a significant portion of the capital expenditures and replacement power costs. Replacement power costs of up to $4.5 million weekly are covered by insurance after March 17, 2021. Insurance recoveries related to replacement power costs will be reflected in electric operating revenues and included in net energy costs under the FAC. Insurance recoveries related to the capital expenditures will be reflected as a reduction to property, plant, and equipment. Ameren Missouri continues to review other legal remedies available.

Insurance

The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at April 1, 2021:

Type and Source of Coverage	Most Recent Renewal Date	Maximum Coverages			Maximum Assessments for Single Incidents
Public liability and nuclear worker liability:
American Nuclear Insurers	January 1, 2021	$	450		$	—
Pool participation	(a)	13,210		(a)	138		(b)
		$	13,660	(c)	$	138
Property damage:
NEIL and EMANI	April 1, 2021	$	3,200	(d)	$	25	(e)
Replacement power:
NEIL	April 1, 2021	$	490	(f)	$	7	(e)

(a)Provided through mandatory participation in an industrywide retrospective premium assessment program. The maximum coverage available is dependent on the number of United States commercial reactors participating in the program.

(b)Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $450 million in the event of an incident at any licensed United States commercial reactor, payable at $21 million per year.

(c)Limit of liability for each incident under the Price-Anderson liability provisions of the Atomic Energy Act of 1954, as amended. This limit is subject to change to account for the effects of inflation and changes in the number of licensed power reactors.

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(d)NEIL provides $2.7 billion in property damage, stabilization, decontamination, and premature decommissioning insurance for radiation events and $2.3 billion in property damage insurance for nonradiation events. EMANI provides $490 million in property damage insurance for both radiation and nonradiation events.

(e)All NEIL-insured plants could be subject to assessments should losses exceed the accumulated funds from NEIL.

(f)Provides replacement power cost insurance in the event of a prolonged accidental outage. Weekly indemnity up to $4.5 million for 52 weeks, which commences after the first 12 weeks of an outage, plus up to $3.6 million per week for a minimum of 71 weeks thereafter for a total not exceeding the policy limit of $490 million. Nonradiation events are limited to $328 million.

The Price-Anderson Act is a federal law that limits the liability for claims from an incident involving any licensed United States commercial nuclear energy center. The limit is based on the number of licensed reactors. The limit of liability and the maximum potential annual payments are adjusted at least every five years for inflation to reflect changes in the Consumer Price Index. The most recent five-year inflationary adjustment became effective in November 2018. Owners of a nuclear reactor cover this exposure through a combination of private insurance and mandatory participation in a financial protection pool, as established by the Price-Anderson Act.

Losses resulting from terrorist attacks on nuclear facilities insured by NEIL are subject to industrywide aggregates, such that terrorist acts against one or more commercial nuclear power plants within a stated time period would be treated as a single event, and the owners of the nuclear power plants would share the limit of liability. NEIL policies have an aggregate limit of $3.2 billion within a 12-month period for radiation events, or $1.8 billion for events not involving radiation contamination, resulting from terrorist attacks. The EMANI policies are not subject to industrywide aggregates in the event of terrorist attacks on nuclear facilities.

If losses from a nuclear incident at the Callaway Energy Center exceed the limits of, or are not covered by insurance, or if coverage is unavailable, Ameren Missouri is at risk for any uninsured losses. If a serious nuclear incident were to occur, it could have a material adverse effect on Ameren’s and Ameren Missouri’s results of operations, financial position, or liquidity.

NOTE 11 – RETIREMENT BENEFITS

The following table presents the components of the net periodic benefit cost (income) incurred for Ameren’s pension and postretirement benefit plans for the three months ended March 31, 2021 and 2020:

	Pension Benefits				Postretirement Benefits
	Three Months				Three Months
	2021		2020		2021		2020
Service cost(a)	$	33	$	27	$	6	$	4
Non-service cost components:
Interest cost	38		43		8		10
Expected return on plan assets	(75)		(73)		(20)		(20)
Amortization of:
Prior service benefit	—		—		(1)		(1)
Actuarial loss (gain)	17		14		(1)		(2)
Total non-service cost components(b)	$	(20)	$	(16)	$	(14)	$	(13)
Net periodic benefit cost (income)	$	13	$	11	$	(8)	$	(9)

(a)Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income.

(b)Non-service cost components are reflected in “Other Income, Net” on Ameren’s statement of income. See Note 5 – Other Income, Net, for additional information.

Ameren Missouri and Ameren Illinois are responsible for their respective share of Ameren’s pension and other postretirement costs. The following table presents the respective share of net periodic pension and other postretirement benefit costs (income) incurred for the three months ended March 31, 2021 and 2020:

	Pension Benefits				Postretirement Benefits
	Three Months				Three Months
	2021		2020		2021		2020
Ameren Missouri(a)	$	6	$	4	$	(1)	$	(1)
Ameren Illinois	8		7		(7)		(8)
Other	(1)		—		—		—
Ameren(a)	$	13	$	11	$	(8)	$	(9)

(a)Does not include the impact of the regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates.

Funding

Based on its assumptions at March 31, 2021, its investment performance in 2021, and its pension funding policy, the estimated aggregate contributions through 2025 has not changed from the $60 million expected aggregate contributions at December 31, 2020.

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NOTE 12 – INCOME TAXES

The following table presents a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the three months ended March 31, 2021 and 2020:

	Ameren		Ameren Missouri		Ameren Illinois
	2021	2020	2021	2020	2021	2020
Three Months
Federal statutory corporate income tax rate:	21%	21%	21%	21%	21%	21%
Increases (decreases) from:
Amortization of deferred investment tax credit	(1)	—	(1)	(1)	—	—
Amortization of excess deferred taxes	(9)	(9)	(17)	(15)	(2)	(3)
Depreciation differences	—	(1)	1	—	(1)	(1)
Renewable and other tax credits	(6)	—	(11)	—	—	—
State tax	6	6	3	3	7	7
Stock-based compensation	(1)	(5)	—	—	—	—
Effective income tax rate	10%	12%	(4)%	8%	25%	24%

NOTE 13 – SUPPLEMENTAL INFORMATION

Cash, Cash Equivalents, and Restricted Cash

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows as of March 31, 2021, and December 31, 2020:

	March 31, 2021						December 31, 2020
	Ameren		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois
Cash and cash equivalents	$	6	$	1	$	—	$	139	$	136	$	—
Restricted cash	134		—		125		17		—		6
Restricted cash included in “Other current assets”	—		3		—		—		5		—
Restricted cash included in “Other assets”	24		—		24		141		—		141
Restricted cash included in “Nuclear decommissioning trust fund”	8		8		—		4		4		—
Total cash, cash equivalents, and restricted cash	$	172	$	12	$	149	$	301	$	145	$	147

Restricted cash included in “Other current assets” primarily represents funds held by an irrevocable Voluntary Employee Beneficiary Association (VEBA) trust, which provides health care benefits for active employees. As of December 31, 2020, restricted cash included in “Other assets” on Ameren’s and Ameren Illinois’ balance sheets primarily represents amounts collected under a cost recovery rider restricted for use in the procurement of renewable energy credits and amounts in a trust fund restricted for the use of funding certain asbestos-related claims. As of March 31, 2021, the amounts collected under a cost recovery rider restricted for use in Ameren Illinois’ procurement of renewable energy credits was reclassified to current as the amount is expected to be refunded to customers within a year.

Accounts Receivable

“Accounts receivable – trade” on Ameren’s and Ameren Illinois’ balance sheets include certain receivables purchased at a discount from alternative retail electric suppliers that elect to participate in the utility consolidated billing program. At March 31, 2021, and December 31, 2020, “Other current liabilities” on Ameren’s and Ameren Illinois’ balance sheets included payables for purchased receivables of $31 million and $28 million, respectively.

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The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the three months ended March 31, 2021 and 2020:

	Three Months
	2021		2020
Ameren:
Beginning of period	$	50	$	17
Bad debt expense	4		3
Net write-offs	(7)		(1)
End of period	$	47	$	19
Ameren Missouri:
Beginning of period	$	16	$	7
Bad debt expense	1		2
Net write-offs	(2)		(1)
End of period	$	15	$	8
Ameren Illinois:(a)
Beginning of Period	$	34	$	10
Bad debt expense	3		1
Net write-offs	(5)		—
End of Period	$	32	$	11

(a)Ameren Illinois has rate-adjustment mechanisms that allow it to recover the difference between its actual net bad debt write-offs under GAAP, including those associated with receivables purchased from alternative retail electric suppliers, and the amount of net bad debt write-offs included in its base rates.

Net write-offs increased for the three months ended March 31, 2021, compared with the year-ago period, due to the resumption of disconnection activities for nonpayment. See Note 2 – Rate and Regulatory Matters for additional information.

Supplemental Cash Flow Information

The following table provides noncash financing and investing activity excluded from the statements of cash flows for the three months ended March 31, 2021 and 2020:

	March 31, 2021						March 31, 2020
	Ameren		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois
Investing
Accrued capital expenditures, including wind generation expenditures	$	271	$	141	$	139	$	235	$	97	$	127
Accrued nuclear fuel expenditures	—		—		—		7		7		—
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund	22		22		—		(111)		(111)		—
Financing
Issuance of common stock for stock-based compensation	33		—		—		38		—		—

Asset Retirement Obligations

The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the three months ended March 31, 2021:

	Ameren Missouri			Ameren Illinois			Ameren
Balance at December 31, 2020	$	751		$	5	(a)	$	756	(b)
Liabilities incurred (c)	10			—			10
Liabilities settled	(3)			—			(3)
Accretion	8		(d)	—			8		(d)
Change in estimates	(7)		(e)	—			(7)		(e)
Balance at March 31, 2021	$	759		$	5	(a)	$	764	(b)

(a)Included in “Other deferred credits and liabilities” on the balance sheet.

(b)Balance included $59 million and $60 million in “Other current liabilities” on the balance sheet as of March 31, 2021, and December 31, 2020, respectively.

(c)In the first quarter of 2021, Ameren Missouri recorded an ARO related to the decommissioning for the Atchison Renewable Energy Center.

(d)Accretion expense attributable to Ameren Missouri was recorded as a decrease to regulatory liabilities.

(e)Ameren Missouri changed its fair value estimate primarily due to a decrease in the cost estimate for closure of certain CCR storage facilities.

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Stock-based Compensation

On January 1, 2021, Ameren granted 293,058 performance share units with a grant date fair value of $25 million and 125,562 restricted share units with a grant date fair value of $10 million. Awards vest approximately 38 months after the grant date or on a pro-rata basis upon death or eligible retirement. The performance share units vest based on the achievement of certain specified market performance measures (251,177 performance share units) or based on the achievement of renewable generation and energy storage installation targets (41,881 performance share units). The exact number of shares issued pursuant to a performance share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the performance goals.

For the three months ended March 31, 2021 and 2020, excess tax benefits associated with the settlement of stock-based compensation awards reduced income tax expense by $5 million and $8 million, respectively.

Deferred Compensation

As of both March 31, 2021, and December 31, 2020, the present value of benefits to be paid for deferred compensation obligations was $90 million, which was primarily reflected in “Other deferred credits and liabilities” on Ameren's consolidated balance sheet.

Operating Revenues

As of March 31, 2021 and 2020, our remaining performance obligations for contracts with a term greater than one year were immaterial. The Ameren Companies elected not to disclose the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied as of the end of the reporting period for contracts with an initial expected term of one year or less.

See Note 14 – Segment Information for disaggregated revenue information.

Excise Taxes

Ameren Missouri and Ameren Illinois collect from their customers excise taxes, including municipal and state excise taxes and gross receipts taxes that are levied on the sale or distribution of natural gas and electricity. The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the three months ended March 31, 2021 and 2020:

	Three Months
	2021		2020
Ameren Missouri	$	31	$	30
Ameren Illinois	39		35
Ameren	$	70	$	65

Earnings per Share

The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three months ended March 31, 2021 and 2020:

	Three Months
	2021	2020
Weighted-average Common Shares Outstanding – Basic	254.4	246.4
Assumed settlement of performance share units and restricted stock units	1.5	1.1
Dilutive effect of forward sale agreement	—	0.6
Weighted-average Common Shares Outstanding – Diluted(a)	255.9	248.1

(a)There were no potentially dilutive securities excluded from the earnings per diluted share calculations for the three months ended March 31, 2021 and 2020.

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NOTE 14 – SEGMENT INFORMATION

The following tables present revenues, net income (loss) attributable to common shareholders, and capital expenditures by segment at Ameren and Ameren Illinois for the three months ended March 31, 2021 and 2020. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount. For additional information about our segments, see Note 16 – Segment Information under Part II, Item 8, of the Form 10-K.

Ameren

	Ameren Missouri			Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission			Other		Intersegment Eliminations		Ameren
Three Months 2021:
External revenues	$	695		$	411	$	347	$	113		$	—	$	—	$	1,566
Intersegment revenues	9			—		—		17			—		(26)		—
Net income attributable to Ameren common shareholders	47			46		75		47		(a)	18		—		233
Capital expenditures	534		(b)	157		48		141			1		6		887		(b)
Three Months 2020:
External revenues	$	670		$	389	$	271	$	110		$	—	$	—	$	1,440
Intersegment revenues	10			1		—		13			—		(24)		—
Net income (loss) attributable to Ameren common shareholders	(10)			37		55		47		(a)	17		—		146
Capital expenditures	278			123		61		170			3		1		636

(a)Ameren Transmission earnings reflect an allocation of financing costs from Ameren (parent).

(b)Includes $193 million at Ameren and Ameren Missouri for wind generation expenditures for the three months ended March 31, 2021.

Ameren Illinois

	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Intersegment Eliminations		Ameren Illinois
Three Months 2021:
External revenues	$	411	$	347	$	65	$	—	$	823
Intersegment revenues	—		—		16		(16)		—
Net income available to common shareholder	46		75		28		—		149
Capital expenditures	157		48		132		—		337
Three Months 2020:
External revenues	$	390	$	271	$	62	$	—	$	723
Intersegment revenues	—		—		12		(12)		—
Net income available to common shareholder	37		55		28		—		120
Capital expenditures	123		61		140		—		324

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The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three months ended March 31, 2021 and 2020. Economic factors affect the nature, timing, amount, and uncertainty of revenues and cash flows in a similar manner across customer classes. Revenues from alternative revenue programs have a similar distribution among customer classes as revenues from contracts with customers. Other revenues not associated with contracts with customers are presented in the Other customer classification, along with electric transmission and off-system revenues.

Ameren

	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Intersegment Eliminations		Ameren
Three Months 2021:
Residential	$	312	$	229	$	—	$	—	$	—	$	541
Commercial	216		132		—		—		—		348
Industrial	52		34		—		—		—		86
Other	61		16		—		130		(26)		181
Total electric revenues	$	641	$	411	$	—	$	130	$	(26)	$	1,156
Residential	$	34	$	—	$	251	$	—	$	—	$	285
Commercial	15		—		64		—		—		79
Industrial	1		—		14		—		—		15
Other	13		—		18		—		—		31
Total natural gas revenues	$	63	$	—	$	347	$	—	$	—	$	410
Total revenues(a)	$	704	$	411	$	347	$	130	$	(26)	$	1,566
Three Months 2020:
Residential	$	297	$	220	$	—	$	—	$	—	$	517
Commercial	221		126		—		—		—		347
Industrial	53		35		—		—		—		88
Other	60		9		—		123		(24)		168
Total electric revenues	$	631	$	390	$	—	$	123	$	(24)	$	1,120
Residential	$	33	$	—	$	213	$	—	$	—	$	246
Commercial	13		—		54		—		—		67
Industrial	1		—		3		—		—		4
Other	2		—		1		—		—		3
Total natural gas revenues	$	49	$	—	$	271	$	—	$	—	$	320
Total revenues(a)	$	680	$	390	$	271	$	123	$	(24)	$	1,440

(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three months ended March 31, 2021 and 2020:

	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Ameren
Three Months 2021:
Revenues from alternative revenue programs	$	(10)	$	61	$	3	$	(1)	$	53
Other revenues not from contracts with customers	(2)		3		1		—		2
Three Months 2020:
Revenues from alternative revenue programs	$	(3)	$	46	$	11	$	12	$	66
Other revenues not from contracts with customers	8		1		1		—		10

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Ameren Illinois

	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Intersegment Eliminations		Ameren Illinois
Three Months 2021:
Residential	$	229	$	251	$	—	$	—	$	480
Commercial	132		64		—		—		196
Industrial	34		14		—		—		48
Other	16		18		81		(16)		99
Total revenues(a)	$	411	$	347	$	81	$	(16)	$	823
Three Months 2020:
Residential	$	220	$	213	$	—	$	—	$	433
Commercial	126		54		—		—		180
Industrial	35		3		—		—		38
Other	9		1		74		(12)		72
Total revenues(a)	$	390	$	271	$	74	$	(12)	$	723

(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three months ended March 31, 2021 and 2020:

	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Ameren Illinois
Three Months 2021:
Revenues from alternative revenue programs	$	61	$	3	$	(1)	$	63
Other revenues not from contracts with customers	3		1		—		4
Three Months 2020:
Revenues from alternative revenue programs	$	46	$	11	$	10	$	67
Other revenues not from contracts with customers	1		1		—		2

ITEM 2. MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS.

The following discussion should be read in conjunction with the financial statements and Risk Factors contained in this Form 10-Q, as well as Management’s Discussion and Analysis of Financial Condition and Results of Operations and Risk Factors contained in the Form 10-K. We intend for this discussion to provide the reader with information that will assist in understanding our financial statements, the changes in certain key items in those financial statements, and the primary factors that accounted for those changes, as well as how certain accounting principles affect our financial statements. The discussion also provides information about the financial results of our business segments to provide a better understanding of how those segments and their results affect the financial condition and results of operations of Ameren as a whole. Also see the Glossary of Terms and Abbreviations at the front of this report and in the Form 10-K.

Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren has other subsidiaries that conduct other activities, such as providing shared services.

•Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri.

•Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois.

•ATXI operates a FERC rate-regulated electric transmission business in the MISO.

Ameren’s financial statements are prepared on a consolidated basis and therefore include the accounts of its majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Missouri and Ameren Illinois have no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated.

In addition to presenting results of operations and earnings amounts in total, we present certain information in cents per share. These amounts reflect factors that directly affect Ameren’s earnings. We believe this per share information helps readers to understand the impact of these factors on Ameren’s earnings per share.

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OVERVIEW

Net income attributable to Ameren common shareholders in the three months ended March 31, 2021, was $233 million, or $0.91 per diluted share, compared with $146 million, or $0.59 per diluted share, in the year-ago period. Net income for the three months ended March 31, 2021, compared to the year-ago period, was favorably affected by the results of Ameren Missouri’s March 2020 electric rate order, infrastructure investments that drove higher earnings at Ameren Transmission and Ameren Illinois Electric Distribution, and increased earnings at Ameren Illinois Natural Gas as a result of a change in rate design, which concentrates more revenues in the winter heating season due to an increase in volumetric rates and a decrease in fixed customer rates, and higher delivery service rates. Earnings for the three months ended March 31, 2021, compared to the year-ago period, were also favorably affected by lower other operations and maintenance expenses not subject to riders or regulatory tracking mechanisms, primarily due to changes in the value of company owned life insurance and disciplined cost management; increased Ameren Missouri electric retail sales, primarily resulting from colder winter temperatures experienced in 2021; and increased income tax benefit at Ameren (parent) and Ameren Missouri due to timing differences associated with certain income tax benefits, which is not expected to materially impact full year results. Net income for the three months ended March 31, 2021, compared to the year-ago period, was unfavorably affected by the result of the March 2021 FERC order, primarily related to the historical recovery of materials and supplies inventories, which decreased Ameren Transmission earnings; the effect of dilution; and higher financing costs at Ameren (parent).

Ameren’s strategic plan includes investing and operating its utilities in a manner consistent with existing regulatory frameworks, enhancing those frameworks, and advocating for responsible energy and economic policies, as well as creating and capitalizing on opportunities for investment for the benefit of its customers, shareholders, and the environment. Ameren remains focused on disciplined cost management and strategic capital allocation. Ameren invested $0.9 billion in its rate-regulated businesses in the three months ended March 31, 2021.

The COVID-19 pandemic continues to affect our results of operations, financial position, and liquidity, but we expect a gradual improvement in sales volumes in 2021, compared to 2020. In the first three months of 2021, our sales volumes were comparable to the same period in 2020, excluding the estimated effects of weather and customer energy-efficiency programs. However, we experienced an increase in our accounts receivable balances that were past due or that were a part of a deferred payment arrangement, and a decline in our cash collections from customers. The continued effect of the COVID-19 pandemic on our results of operations, financial position, and liquidity in subsequent periods will depend on its severity and longevity, future regulatory or legislative actions with respect thereto, and the resulting impact on business, economic, and capital market conditions. In general, restrictions on social activities and nonessential businesses implemented in our service territories in 2020 have been relaxed. However, certain restrictions remain in place that limit individual activities and the operation of nonessential businesses and additional restrictions may be imposed in the future. We continue to assess the impacts the COVID-19 pandemic is having on our businesses, including impacts on electric and natural gas sales volumes, liquidity, bad debt expense, and supply chain operations. For further discussion of these and other matters, see Note 2 – Rate and Regulatory Matters under Part I, Item 1, of this report, and Results of Operations, Liquidity and Capital Resources, and Outlook sections below. In addition, for information regarding Ameren Illinois’ suspension and subsequent reinstatement of customer disconnection activities and late fee charges for nonpayment, see Note 2 – Rate and Regulatory Matters under Part I, Item 1, of this report.

In January 2021, Ameren Missouri acquired an up-to 300-MW wind generation project located in northwestern Missouri and partially placed it in service as the Atchison Renewable Energy Center. As of the date of this filing, Ameren Missouri has placed approximately half of the project in service, representing a purchase price of approximately $250 million, including an immaterial amount of transaction costs. Ameren Missouri expects the remaining MWs of the project to be in service by the end of September 2021. The Atchison Renewable Energy Center will support Ameren Missouri’s compliance with the Missouri renewable energy standard.

In February 2021, Ameren Missouri filed an update to its Smart Energy Plan with the MoPSC, which includes a five-year capital investment overview with a detailed one-year plan for 2021. The plan is designed to upgrade Ameren Missouri’s electric infrastructure and includes investments that will upgrade the grid and accommodate more renewable energy. Investments under the plan are expected to total approximately $8.4 billion over the five-year period from 2021 through 2025, with expenditures largely recoverable under the PISA and the RESRAM. The planned investments in 2024 and 2025 are based on the assumption that Ameren Missouri requests and receives MoPSC approval of an extension of the PISA through December 2028.

In March 2021, Ameren Missouri filed a request with the MoPSC seeking approval to increase its annual revenues for electric service by $299 million. The electric rate increase request is based on a 9.9% ROE, a capital structure composed of 51.9% common equity, a rate base of $10.0 billion and a test year ended December 31, 2020, with certain pro-forma adjustments expected through an anticipated true-up date of September 30, 2021. The MoPSC proceeding relating to the proposed electric service rate changes will take place over a period of up to 11 months, with a decision by the MoPSC expected by February 2022 and new rates effective by March 2022. See Note 2 – Rate and Regulatory Matters under Part I, Item 1, of this report for additional information.

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In March 2021, Ameren Missouri filed a request with the MoPSC seeking approval to increase its annual revenues for natural gas delivery service by $9 million. The natural gas rate increase request is based on a 9.8% ROE, a capital structure composed of 51.9% common equity, a rate base of $310 million, and a test year ended December 31, 2020, with certain pro-forma adjustments expected through an anticipated true-up date of September 30, 2021. The MoPSC proceeding relating to the proposed natural gas delivery service rate changes will take place over a period of up to 11 months with a decision by the MoPSC expected by February 2022 and new rates effective by March 2022.

In March 2021, the MoPSC issued orders approving nonunanimous stipulation and agreements related to Ameren Missouri’s electric and natural gas service accounting authority order requests. The orders allowed Ameren Missouri to accumulate $9 million of certain costs incurred related to the COVID-19 pandemic, net of cost savings, as well as forgone customer late fee and reconnection fee revenues from March 2020 to March 2021, for potential recovery in the electric and natural gas service regulatory rate reviews discussed above. As of March 31, 2021, Ameren Missouri deferred $5 million as a regulatory asset related to the accounting authority orders. If approved for recovery, Ameren Missouri would recognize the remaining $4 million associated with forgone customer late fee and reconnection fee revenue when billed to customers.

In March 2021, the ICC issued an order approving Ameren Illinois’ requested tariff to reconcile its electric distribution service revenue requirement for a period of up to two years after the final customer rate update under performance-based formula ratemaking. To utilize the reconciliation, the ICC-approved tariff requires Ameren Illinois to file a traditional regulatory rate review for its electric distribution service, which may be based on a future test year, by the end of March in the year following the last year in which an annual performance-based formula rate update was permitted. Pursuant to this order, and without legislative change or Ameren Illinois’ election to no longer use performance-based formula ratemaking, Ameren Illinois’ 2022 and 2023 revenues would reflect each year’s actual costs, year-end rate base, and a return at the applicable WACC, with the ROE based on the annual average of the monthly yields of the 30-year United States Treasury bonds plus 580 basis points. The revenue requirement adjustment will be collected from, or refunded to, customers within two years from the end of the reconciled year.

In March 2021, Ameren Illinois filed with the ICC an energy-efficiency plan which includes annual investments in electric energy-efficiency programs up to approximately $100 million per year from 2022 through 2025. The ICC has the ability to reduce the amount of electric energy-efficiency savings goals in future plan program years if there are insufficient cost-effective programs available, which could reduce the investments in electric energy-efficiency programs. The electric energy-efficiency program investments and the return on those investments are collected from customers through a rider and are not included in the electric distribution service performance-based formula ratemaking framework. A decision by the ICC in this proceeding is expected by September 2021.

In April 2021, Ameren Illinois filed its annual electric distribution service performance-based formula rate update with the ICC, requesting an increase of $64 million in its rates. This update reflects an increase to the annual performance-based formula rate based on 2020 actual costs, an increase to include the 2020 revenue requirement reconciliation adjustment, and an increase for the conclusion of the 2019 revenue requirement reconciliation adjustment, which will be fully refunded to customers in 2021, consistent with the ICC’s December 2020 annual update filing order. It also reflects an increase based on expected net plant additions for 2021. An ICC decision in this proceeding is expected by December 2021, with new rates effective January 2022.

RESULTS OF OPERATIONS

Our results of operations and financial position are affected by many factors. Economic conditions, including those resulting from the COVID-19 pandemic discussed below, energy-efficiency investments by our customers and by us, technological advances, distributed generation, and the actions of key customers can significantly affect the demand for our services. Ameren and Ameren Missouri results are also affected by seasonal fluctuations in winter heating and summer cooling demands, as well as by non-nuclear energy center maintenance outages. Additionally, fluctuations in interest rates and conditions in the capital and credit markets affect our cost of borrowing, and our pension and postretirement benefits costs. Almost all of Ameren’s revenues are subject to state or federal regulation. This regulation has a material impact on the rates we charge customers for our services. Our results of operations, financial position, and liquidity are affected by our ability to align our overall spending, both operating and capital, with the frameworks established by our regulators. See Note 2 – Rate and Regulatory Matters under Part I, Item 1, of this report and Note 2 – Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K for additional information regarding Ameren Missouri’s, Ameren Illinois’, and ATXI’s regulatory mechanisms.

We continue to assess the impacts of the COVID-19 pandemic on our businesses, including impacts on electric and natural gas sales volumes, supply chain operations, and bad debt expense. Regarding uncollectible accounts receivable, Ameren Illinois’ electric distribution and natural gas distribution businesses have bad debt riders, which provide for recovery of bad debt write-offs, net of any subsequent recoveries. Ameren Missouri does not have a bad debt rider or tracker, and thus its earnings are exposed to increases in bad debt expense, absent regulatory relief. However, Ameren Missouri does not expect a material impact to earnings from increases in bad debt expense. As of March 31, 2021, accounts receivable balances that were 30 days or greater past due or that were a part of a deferred payment arrangement represented 27%, 19%, and 32%, or $137 million, $33 million, and $104 million, of Ameren’s, Ameren Missouri’s, and Ameren Illinois’

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customer trade receivables before allowance for doubtful accounts, respectively. As of March 31, 2020, these percentages were 21%, 16%, and 25%, or $99 million, $29 million, and $70 million, for Ameren, Ameren Missouri, and Ameren Illinois, respectively. Ameren Missouri's electric sales volumes have been, and continue to be, affected by the COVID-19 pandemic. In the three months ended March 31, 2021, compared to the same period in 2020, Ameren Missouri experienced a reduction in commercial and industrial electric sales volumes, offset by increased electric sales volumes to higher margin residential customers, excluding the estimated effects of weather and customer energy-efficiency programs. The following table provides the increases and (decreases) in Ameren Missouri electric sales volumes by customer class for the three months ended March 31, 2021, compared to the same period in 2020, excluding the estimated effects of weather and customer energy-efficiency programs:

	Three months ended March 31, 2021, versus same period in 2020
Ameren Missouri Customer Class
Residential	2.7	%
Commercial	(2.8)	%
Industrial	(1.2)	%
Total	(0.1)	%

Ameren Missouri principally uses coal and enriched uranium for fuel in its electric operations and purchases natural gas for its customers. Ameren Illinois purchases power and natural gas for its customers. The prices for these commodities can fluctuate significantly because of the global economic and political environment, weather, supply, demand, and many other factors. We have natural gas cost recovery mechanisms for our Illinois and Missouri natural gas distribution businesses, a purchased power cost recovery mechanism for Ameren Illinois’ electric distribution business, and a FAC for Ameren Missouri’s electric business.

We employ various risk management strategies to reduce our exposure to commodity risk and other risks inherent in our business. The reliability of Ameren Missouri’s energy centers and our transmission and distribution systems, and the level and timing of operations and maintenance costs and capital investment, are key factors that we seek to manage in order to optimize our results of operations, financial position, and liquidity.

Earnings Summary

The following table presents a summary of Ameren’s earnings for the three months ended March 31, 2021 and 2020:

	Three Months
	2021		2020
Net income attributable to Ameren common shareholders	$	233	$	146
Earnings per common share – diluted	0.91		0.59

Net income attributable to Ameren common shareholders increased $87 million in the three months ended March 31, 2021, compared with the year-ago period. The increase was due to net income increases of $20 million, $9 million, and $1 million at Ameren Illinois Natural Gas, Ameren Illinois Electric Distribution, and activity not reported as part of a segment, primarily at Ameren (parent), respectively. Additionally, Ameren Missouri had net income of $47 million, compared to a net loss of $10 million in the same period in 2020.

Earnings per diluted share were favorably affected in the three months ended March 31, 2021, compared to the year-ago period, by:

•the results of the March 2020 MoPSC electric rate order, as discussed in Note 2 – Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K, which reduced the base level of expenses at Ameren Missouri, partially offset by lower base rates, net of recovery for amounts associated with the reduction in sales volumes resulting from MEEIA programs and recoverable depreciation under the PISA (10 cents per share);

•decreased other operations and maintenance expense not subject to riders and trackers, primarily due to changes in the cash surrender value of company-owned life insurance and disciplined cost management, partially offset by 2 cents per share due to amortization of costs associated with the Callaway Energy Center’s scheduled refueling and maintenance outage completed in 2020 (6 cents per share);

•increased rate base investments and a higher recognized ROE, which increased earnings at Ameren Transmission and Ameren Illinois Electric Distribution (5 cents per share);

•increased income tax benefit at Ameren (parent), primarily due to increased interim period income tax benefits in 2021 related to wind generation facilities, and at Ameren Missouri primarily due to year-over-year timing differences associated with the recognition of excess deferred income taxes, both of which are not expected to materially impact full year results (4 cents per share);

•the impact of weather on electric retail sales at Ameren Missouri, primarily resulting from colder winter temperatures experienced in 2021 (estimated at 4 cents per share);

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•a change in rate design pursuant to the ICC's January 2021 natural gas rate order that concentrates more revenues in the winter heating season due to an increase in volumetric rates, which increased margins at Ameren Illinois Natural Gas for the three months ended March 31, 2021, but is not expected to materially impact full year results (4 cents per share);

•higher base rates pursuant to the ICC's January 2021 natural gas rate order, which increased margins at Ameren Illinois Natural Gas (3 cents per share); and

•increased other income, net, at Ameren Missouri due to the absence of charitable donations made in 2020 pursuant to the March 2020 electric rate order (2 cents per share).

Earnings per diluted share were unfavorably affected in the three months ended March 31, 2021, compared to the year-ago period, by:

•increased weighted-average basic common shares outstanding and the effect of dilution (4 cents per share);

•the result of the March 2021 FERC order, primarily related to the historical recovery of materials and supplies inventories, which decreased Ameren Transmission earnings (3 cents per share); and

•increased net financing costs at Ameren (parent), primarily due to higher long-term debt balances (2 cents per share).

The cents per share information presented is based on the weighted-average basic common shares outstanding in the three months ended March 31, 2020, and does not reflect any change in earnings per share resulting from dilution, unless otherwise noted. Amounts other than variances related to income taxes have been presented net of income taxes using Ameren’s 2021 statutory tax rate of 26%. For additional details regarding the Ameren Companies’ results of operations, including explanations of Electric and Natural Gas Margins, Other Operations and Maintenance Expenses, Depreciation and Amortization Expenses, Taxes Other Than Income Taxes, Other Income, Net, Interest Charges, and Income Taxes, see the major headings below.

Below is Ameren’s table of income statement components by segment for the three months ended March 31, 2021 and 2020:

	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Other / Intersegment Eliminations		Ameren
Three Months 2021:
Electric margins	$	488	$	289	$	—	$	130	$	(7)	$	900
Natural gas margins	32		—		213		—		—		245
Other operations and maintenance expenses	(225)		(125)		(56)		(16)		2		(420)
Depreciation and amortization expenses	(156)		(75)		(22)		(28)		—		(281)
Taxes other than income taxes	(77)		(20)		(25)		(2)		(4)		(128)
Other income, net	23		8		3		3		9		46
Interest charges	(39)		(18)		(10)		(23)		(10)		(100)
Income (taxes) benefit	2		(12)		(28)		(17)		28		(27)
Net income	48		47		75		47		18		235
Noncontrolling interests – preferred stock dividends	(1)		(1)		—		—		—		(2)
Net income attributable to Ameren common shareholders	$	47	$	46	$	75	$	47	$	18	$	233
Three Months 2020:
Electric margins	$	452	$	280	$	—	$	123	$	(9)	$	846
Natural gas margins	31		—		182		—		—		213
Other operations and maintenance expenses	(239)		(130)		(57)		(14)		2		(438)
Depreciation and amortization expenses	(139)		(71)		(21)		(24)		—		(255)
Taxes other than income taxes	(79)		(19)		(22)		(2)		(3)		(125)
Other income, net	4		7		2		2		6		21
Interest charges	(40)		(18)		(10)		(21)		(4)		(93)
Income (taxes) benefit	1		(11)		(19)		(17)		25		(21)
Net income (loss)	(9)		38		55		47		17		148
Noncontrolling interests – preferred stock dividends	(1)		(1)		—		—		—		(2)
Net income (loss) attributable to Ameren common shareholders	$	(10)	$	37	$	55	$	47	$	17	$	146

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Below is Ameren Illinois’ table of income statement components by segment for the three months ended March 31, 2021 and 2020:

	Ameren Illinois Electric Distribution		Ameren Illinois  Natural Gas		Ameren Illinois Transmission		Ameren Illinois
Three Months 2021:
Electric and natural gas margins	$	289	$	213	$	81	$	583
Other operations and maintenance expenses	(125)		(56)		(13)		(194)
Depreciation and amortization expenses	(75)		(22)		(18)		(115)
Taxes other than income taxes	(20)		(25)		(1)		(46)
Other income, net	8		3		3		14
Interest charges	(18)		(10)		(14)		(42)
Income taxes	(12)		(28)		(10)		(50)
Net income	47		75		28		150
Preferred stock dividends	(1)		—		—		(1)
Net income attributable to common shareholder	$	46	$	75	$	28	$	149
Three Months 2020:
Electric and natural gas margins	$	280	$	182	$	74	$	536
Other operations and maintenance expenses	(130)		(57)		(12)		(199)
Depreciation and amortization expenses	(71)		(21)		(15)		(107)
Taxes other than income taxes	(19)		(22)		(1)		(42)
Other income, net	7		2		2		11
Interest charges	(18)		(10)		(11)		(39)
Income taxes	(11)		(19)		(9)		(39)
Net income	38		55		28		121
Preferred stock dividends	(1)		—		—		(1)
Net income attributable to common shareholder	$	37	$	55	$	28	$	120

Electric and Natural Gas Margins

Electric margins are defined as electric revenues less fuel and purchased power costs. Natural gas margins are defined as natural gas revenues less natural gas purchased for resale. We consider electric and natural gas margins useful measures to analyze the change in profitability of our electric and natural gas operations between periods. We have included the analysis below to complement the financial information we provide in accordance with GAAP. However, these margins may not be a presentation defined under GAAP, and they may not be comparable to other companies’ presentations or more useful than the GAAP information we provide elsewhere in this report.

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Electric Margins

	Increase (Decrease) by Segment
Total by Segment(a)	Overall Ameren Increase of $54 Million

(a)Includes other/intersegment eliminations of $(7) million and $(9) million in the three months ended March 31, 2021 and 2020, respectively.

Ameren Missouri Ameren Illinois Electric Distribution Ameren Transmission Other/Intersegment Eliminations

Natural Gas Margins

	Increase (Decrease) by Segment
Total by Segment	Overall Ameren Increase of $32 Million

Ameren Missouri Ameren Illinois Natural Gas

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The following table present the favorable (unfavorable) variations by Ameren segment for electric and natural gas margins for the three months ended March 31, 2021, compared with the year-ago period:

Three Months	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission(a)		Other /Intersegment Eliminations		Ameren
Electric revenue change:
Effect of weather (estimate)(b)	$	18	$	—	$	—	$	—	$	—	$	18
Base rates (estimate)(c)	(6)		3		—		7		—		4
Sales volumes and changes in customer usage patterns (excluding the estimated effects of weather and MEEIA)	(3)		—		—		—		—		(3)
Off-system sales, capacity and FAC revenues, net	(4)		—		—		—		—		(4)
Energy-efficiency program investments	—		3		—		—		—		3
Other	(4)		4		—		—		(2)		(2)
Cost recovery mechanisms – offset in fuel and purchased power(d)	3		12		—		—		—		15
Other cost recovery mechanisms(e)	6		(1)		—		—		—		5
Total electric revenue change	$	10	$	21	$	—	$	7	$	(2)	$	36
Fuel and purchased power change:
Effect of weather (estimate)(b)	$	(5)	$	—	$	—	$	—	$	—	$	(5)
Effect of lower net energy costs included in base rates	36		—		—		—		—		36
Other	(2)		—		—		—		4		2
Cost recovery mechanisms – offset in electric revenue(d)	(3)		(12)		—		—		—		(15)
Total fuel and purchased power change	$	26	$	(12)	$	—	$	—	$	4	$	18
Net change in electric margins	$	36	$	9	$	—	$	7	$	2	$	54
Natural gas revenue change:
Effect of weather (estimate)(b)	$	(3)	$	—	$	—	$	—	$	—	$	(3)
Base rates (estimate)	—		—		12		—		—		12
Change in rate design	—		—		12		—		—		12
Other	—		—		3		—		—		3
Cost recovery mechanisms – offset in natural gas purchased for resale(d)	17		—		45		—		—		62
Other cost recovery mechanisms(e)	—		—		4		—		—		4
Total natural gas revenue change	$	14	$	—	$	76	$	—	$	—	$	90
Natural gas purchased for resale change:
Effect of weather (estimate)(b)	$	4	$	—	$	—	$	—	—		$	4
Cost recovery mechanisms – offset in natural gas revenue(d)	(17)		—		(45)		—		—		(62)
Total natural gas purchased for resale change	$	(13)	$	—	$	(45)	$	—	$	—	$	(58)
Net change in natural gas margins	$	1	$	—	$	31	$	—	$	—	$	32

(a)Includes an increase in transmission margins of $7 million at Ameren Illinois for the three months ended March 31, 2021, compared with the year-ago period.

(b)Represents the estimated variation resulting primarily from changes in cooling and heating degree-days on electric and natural gas demand compared with the year-ago period; this variation is based on temperature readings from the National Oceanic and Atmospheric Administration weather stations at local airports in our service territories.

(c)For Ameren Illinois Electric Distribution and Ameren Transmission, base rates include increases or decreases to operating revenues related to the revenue requirement reconciliation adjustment under formula rates. For Ameren Missouri, base rates exclude an increase of $7 million for the recovery of lost electric margins for the three months ended March 31, 2021, compared with the year-ago period, resulting from the MEEIA 2016 and 2019 customer energy-efficiency programs. This amount is included in the “sales volumes and changes in customer usage patterns (excluding the estimated effects of weather and MEEIA)” line item.

(d)Electric and natural gas revenue changes are offset by corresponding changes in “Fuel,” “Purchased power,” and “Natural gas purchased for resale” on the statement of income, resulting in no change to electric and natural gas margins.

(e)Offsetting expense increases or decreases are reflected in “Other operations and maintenance,” “Depreciation and amortization,” or in “Taxes other than income taxes,” within the “Operating Expenses” section and "Income Taxes" in the statement of income. These items have no overall impact on earnings.

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Ameren

Ameren’s electric margins increased $54 million, or 6%, for the three months ended March 31, 2021, compared with the year-ago period, primarily because of increased margins at Ameren Missouri, Ameren Illinois Electric Distribution, and Ameren Transmission, as discussed below. Ameren’s natural gas margins increased $32 million, or 15%, for the three months ended March 31, 2021, compared with the year-ago period, primarily because of increased margins at Ameren Illinois Natural Gas, as discussed below.

Ameren Transmission

Ameren Transmission’s margins increased $7 million, or 6%, for the three months ended March 31, 2021, compared with the year-ago period. Base rate revenues were favorably affected by increased capital investment, as evidenced by a 11% increase in rate base used to calculate the revenue requirement, partially offset by the March 2021 FERC order, which required refunds related to historical recovery of materials and supplies inventories. See Transmission Formula Rate Revisions in Note 2 – Rate and Regulatory Matters under Part I, Item 1, of this report for additional information regarding the March 2021 FERC order.

Ameren Missouri

Ameren Missouri’s electric margins increased $36 million, or 8%, for the three months ended March 31, 2021, compared with the year ago period.

The following items had a favorable effect on Ameren Missouri’s electric margins between periods:

•The March 2020 MoPSC electric rate order that resulted in lower net energy costs included in base rates partially offset by lower electric base rates increased margins $30 million. The change in electric base rates is the sum of the change in base rates (estimate) (-$6 million) and the effect of lower net energy costs included in base rates (+$36 million) in the table above.

•Winter temperatures were colder as heating degree days increased 12%. The aggregate effect of weather increased margins an estimated $13 million. The change in margins due to weather is the sum of the effect of weather (estimate) on electric revenues (+$18 million) and the effect of weather (estimate) on fuel and purchased power (-$5 million) in the table above.

The following items had an unfavorable effect on Ameren Missouri’s electric margins between periods:

•The absence of the Callaway Energy Center generation and the extremely cold weather in mid-February 2021 drove net energy costs higher than those reflected in base rates, which reduced margins by $4 million, resulting from Ameren Missouri’s 5% exposure to net energy cost variances under the FAC. The change in net energy costs is the sum of the revenue change in “Off-system sales, capacity and FAC revenues, net” (-$4 million) in the table above, and the change in “energy costs” (comparable between periods).

•Excluding the estimated effects of weather and the MEEIA customer energy-efficiency programs, electric revenues decreased an estimated $3 million. The decrease was primarily due to a reduction in the average retail price per kilowatthour due to changes in customer usage patterns and shifts in commercial and industrial usage between rate classes. While the MEEIA customer energy-efficiency programs reduced retail sales volumes, the recovery of lost electric margins under the MEEIA ensured that electric margins were not affected.

Ameren Missouri’s natural gas margins were comparable between periods. Purchased gas costs increased $17 million, primarily resulting from the significant increase in customer demand and prices for natural gas experienced in mid-February 2021 due to the extremely cold weather. The increased purchased gas costs are fully offset by an increase in natural gas revenues under the PGA rider, resulting in no impact to margin. The increase in purchased gas cost is reflected in “cost recovery mechanisms - offset in natural gas revenue” and the associated recoverability from customers is reflected in “cost recovery mechanisms - offset in natural gas purchased for resale”.

Ameren Illinois

Ameren Illinois’ electric margins increased $16 million, or 5%, for the three months ended March 31, 2021, compared with the year-ago period, driven by increased margins at Ameren Illinois Electric Distribution and Ameren Illinois Transmission. Ameren Illinois Natural Gas’ margins increased $31 million, or 17%, between periods.

Ameren Illinois Electric Distribution

Ameren Illinois Electric Distribution’s margins increased $9 million, or 3%, for the three months ended March 31, 2021, compared with the year-ago period. Purchased power costs increased $12 million, primarily resulting from the significant increase in customer demand and prices for electricity experienced in mid-February 2021 due to the extremely cold weather. The increased purchased power costs are fully offset by an increase in electric revenues under the cost recovery mechanisms for purchased power, resulting in no impact to margin. The increase in purchased power cost is reflected in “cost recovery mechanisms - offset in electric revenue” and the associated recoverability

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from customers is reflected in “cost recovery mechanisms - offset in fuel and purchased power”. The following items had a favorable effect on Ameren Illinois Electric Distribution’s margins between periods:

•Margins increased due to a higher recognized ROE (+$4 million), as evidenced by an increase of 72 basis points in the estimated annual average of the monthly yields of the 30-year United States Treasury bonds, and increased capital investment (+$2 million), as evidenced by a 6% increase in rate base used to calculate the revenue requirement, partially offset by lower recoverable non-purchased power expenses (-$3 million). The sum of these changes collectively increased margins $3 million.

•Revenues increased $3 million due to recovery of increased energy-efficiency program investments under performance-based formula ratemaking.

Ameren Illinois Natural Gas

Ameren Illinois Natural Gas’ margins increased $31 million, or 17%, for the three months ended March 31, 2021, compared with the year-ago period. Purchased gas costs increased $45 million, primarily resulting from the significant increase in customer demand and prices for natural gas experienced in mid-February 2021 due to the extremely cold weather. The increased purchased gas costs are fully offset by an increase in natural gas revenues under the PGA rider, resulting in no impact to margin. The increase in purchased gas cost is reflected in “cost recovery mechanisms - offset in natural gas revenue” and the associated recoverability from customers is reflected in “cost recovery mechanisms - offset in natural gas purchased for resale”. The following items had a favorable effect on Ameren Illinois Natural Gas’ margins between periods:

•Revenues increased $12 million due to higher natural gas base rates as a result of the January 2021 natural gas rate order.

•The implementation of a change in rate design pursuant to the January 2021 natural gas rate order, which increased margins $12 million. This change in rate design concentrates more revenues in the winter heating season due to an increase in volumetric rates and a decrease in fixed customer rates. As such, the change is not expected to materially affect annual earnings comparisons.

Ameren Illinois Transmission

Ameren Illinois Transmission’s margins increased $7 million, or 9%, for the three months ended March 31, 2021, compared with the year-ago period. Margins were favorably affected by increased capital investment, as evidenced by a 17% increase in rate base used to calculate the revenue requirement, partially offset by the March 2021 FERC order, which required refunds related to historical recovery of materials and supplies inventories. See Transmission Formula Rate Revisions in Note 2 – Rate and Regulatory Matters under Part I, Item 1, of this report for additional information regarding the March 2021 FERC order.

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Other Operations and Maintenance Expenses

	Increase (Decrease) by Segment
Total by Segment(a)	Overall Ameren Decrease of $18 Million

(a)Includes other/intersegment eliminations of $(2) million and $(2) million in the three months ended March 31, 2021 and 2020, respectively.

Ameren Missouri	Ameren Illinois Natural Gas	Other/Intersegment Eliminations
Ameren Illinois Electric Distribution	Ameren Transmission

Ameren

Other operations and maintenance expenses decreased $18 million in the three months ended March 31, 2021, compared with the year-ago period, due to changes discussed below.

Ameren Transmission

Other operations and maintenance expenses were comparable between periods.

Ameren Missouri

The $14 million decrease in other operations and maintenance expenses in the three months ended March 31, 2021, compared with the year-ago period, was primarily due to the following items:

•The cash surrender value of company-owned life insurance increased $8 million, primarily because of unfavorable market returns in the year-ago period.

•Amortization of costs, primarily solar rebate costs incurred prior to the RESRAM, decreased $6 million pursuant to the March 2020 MoPSC electric rate order.

•Deferral to a regulatory asset of $5 million of certain costs incurred related to the COVID-19 pandemic, pursuant to the March 2021 MoPSC orders.

•Transmission and distribution expenditures decreased $5 million, primarily resulting from less maintenance due to recent capital improvements and disciplined cost management.

The following items partially offset the above decreases in other operations and maintenance expenses between periods:

•Energy center maintenance costs increased $8 million, primarily because of the amortization of Callaway refueling and maintenance costs deferred as a regulatory asset in the year-ago period, pursuant to the February 2020 MoPSC order.

•Customer energy-efficiency program costs increased $6 million because of increased participation in the MEEIA programs in the current period.

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Ameren Illinois

Other operations and maintenance expenses decreased $5 million in the three months ended March 31, 2021, compared with the year-ago period, as discussed below. Other operations and maintenance expenses were comparable between periods at Ameren Illinois Natural Gas and Ameren Illinois Transmission.

Ameren Illinois Electric Distribution

Other operations and maintenance expenses decreased $5 million in the three months ended March 31, 2021, compared with the year-ago period, primarily because of a $4 million increase in the cash surrender value of company-owned life insurance due to unfavorable market returns in the year-ago period. Other operations and maintenance expenses also decreased because of a $3 million reduction in distribution expenditures, resulting from disciplined cost management and timing of expenditures. These decreases were partially offset by a $2 million increase in the amortization of energy-efficiency program investments under performance-based ratemaking.

Depreciation and Amortization Expenses

	Increase (Decrease) by Segment
Total by Segment(a)	Overall Ameren Increase of $26 Million

(a)Includes other/intersegment eliminations of $— million and $— million in the three months ended March 31, 2021 and 2020, respectively.

Ameren Missouri	Ameren Illinois Natural Gas	Other/Intersegment Eliminations
Ameren Illinois Electric Distribution	Ameren Transmission

Depreciation and amortization expenses increased $26 million, $17 million, and $8 million in the three months ended March 31, 2021, compared with the year-ago period, at Ameren, Ameren Missouri, and Ameren Illinois, respectively, primarily because of additional property, plant, and equipment investments across their respective segments. Ameren’s and Ameren Missouri’s depreciation and amortization expenses reflected a deferral to a regulatory asset of depreciation and amortization expenses pursuant to the PISA and RESRAM. The PISA and RESRAM deferrals of depreciation and amortization expenses were $19 million and $13 million for the three months ended March 31, 2021 and 2020, respectively.

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Taxes Other Than Income Taxes

	Increase (Decrease) by Segment
Total by Segment(a)	Overall Ameren Increase of $3 Million

(a)Includes $2 million and $2 million at Ameren Transmission in the three months ended March 31, 2021 and 2020, respectively, and other/intersegment eliminations of $4 million and $3 million in the three months ended March 31, 2021 and 2020, respectively.

Ameren Missouri	Ameren Illinois Natural Gas	Other/Intersegment Eliminations
Ameren Illinois Electric Distribution	Ameren Transmission

Taxes other than income taxes increased $3 million in the three months ended March 31, 2021, compared with the year-ago period, primarily because of a $3 million increase in excise taxes at Ameren Illinois Natural Gas, as a result of increased sales.

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Other Income, Net

	Increase (Decrease) by Segment
Total by Segment	Overall Ameren Increase of $25 Million

Ameren Missouri	Ameren Illinois Natural Gas	Other/Intersegment Eliminations
Ameren Illinois Electric Distribution	Ameren Transmission

Other income, net, increased $25 million in the three months ended March 31, 2021, compared with the year-ago period, primarily because of a $9 million increase in the non-service cost components of net periodic benefit income at Ameren Missouri and an $8 million decrease in charitable donations due to the absence of charitable donations made in the year-ago period pursuant to the March 2020 MoPSC electric rate order. Other income, net, also increased $3 million for activity not reported as part of a segment primarily because of increased income from equity investments.

See Note 5 – Other Income, Net, under Part I, Item 1, of this report for additional information.

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Interest Charges

	Increase (Decrease) by Segment
Total by Segment	Overall Ameren Increase of $7 Million

Ameren Missouri	Ameren Illinois Natural Gas	Other/Intersegment Eliminations
Ameren Illinois Electric Distribution	Ameren Transmission

Interest charges increased $7 million in the three months ended March 31, 2021, compared with the year-ago period, primarily due to a long-term debt issuance at Ameren (parent) in April 2020, which increased interest charges by $7 million. Interest charges at Ameren and Ameren Missouri reflected a deferral to a regulatory asset of interest charges pursuant to PISA and RESRAM. The PISA and RESRAM deferrals of interest charges were $15 million and $9 million for the three months ended March 31, 2021 and 2020, respectively.

Income Taxes

The following table presents effective income tax rates for the three months ended March 31, 2021 and 2020:

	Three Months(a)
	2021		2020
Ameren	10	%	12	%
Ameren Missouri	(4)	%	8	%
Ameren Illinois	25	%	24	%
Ameren Illinois Electric Distribution	22	%	22	%
Ameren Illinois Natural Gas	27	%	26	%
Ameren Illinois Transmission	25	%	24	%
Ameren Transmission	27	%	26	%

(a)Estimate of the annual effective income tax rate adjusted to reflect the tax effect of items discrete to the three months ended March 31, 2021 and 2020.

See Note 12 – Income Taxes under Part I, Item 1, of this report for a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the Ameren Companies.

LIQUIDITY AND CAPITAL RESOURCES

Collections from our tariff-based revenues are our principal source of cash provided by operating activities. A diversified retail customer mix, primarily consisting of rate-regulated residential, commercial, and industrial customers, provides us with a reasonably predictable source of cash. In addition to using cash provided by operating activities, we use available cash, drawings under committed credit agreements, commercial paper issuances, and/or, in the case of Ameren Missouri and Ameren Illinois, short-term affiliate borrowings to support normal operations and temporary capital requirements. We may reduce our short-term borrowings with cash provided by operations or, at our

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discretion, with long-term borrowings, or, in the case of Ameren Missouri and Ameren Illinois, with capital contributions from Ameren (parent). We expect to make significant capital expenditures over the next five years, supported by a combination of long-term debt and equity, as we invest in our electric and natural gas utility infrastructure to support overall system reliability, grid modernization, renewable energy targets requirements, environmental compliance, and other improvements. As part of its plan to fund the cash requirements for capital expenditures, Ameren is using newly issued shares of common stock, rather than market-purchased shares, to satisfy requirements under the DRPlus and employee benefit plans and expects to continue to do so through at least 2025. Ameren expects these issuances to provide equity of about $100 million annually. In addition to the issuance of common shares in connection with the 2021 settlement of the remaining portion of the forward sale agreement, Ameren plans to issue incremental equity of about $150 million in 2021 and about $300 million each year from 2022 to 2025. Ameren expects to establish an at-the-market equity program that will allow Ameren to meet equity needs through 2023, subject to market conditions and other factors. Ameren expects its equity to total capitalization to be about 45% through December 31, 2025, with the long-term intent to support solid investment-grade credit ratings. See Long-term Debt and Equity below and Note 4 – Long-term Debt and Equity Financings under Part I, Item 1, of this report for additional information on the 2021 settlement of the remaining portion of the forward sale agreement.

The use of cash provided by operating activities and short-term borrowings to fund capital expenditures and other long-term investments at the Ameren Companies frequently results in a working capital deficit, defined as current liabilities exceeding current assets, as was the case at March 31, 2021, for Ameren and Ameren Illinois. With the credit capacity available under the Credit Agreements, and cash and cash equivalents, Ameren (parent), Ameren Missouri, and Ameren Illinois, collectively, had net available liquidity of $1.4 billion at March 31, 2021. See Credit Facility Borrowings and Liquidity for additional information.

The following table presents net cash provided by (used in) operating, investing, and financing activities for the three months ended March 31, 2021 and 2020:

	Net Cash Provided By (Used In) Operating Activities						Net Cash Used In Investing Activities						Net Cash Provided By Financing Activities
	2021		2020		Variance		2021		2020		Variance		2021		2020		Variance
Ameren	$	(35)	$	290	$	(325)	$	(889)	$	(684)	$	(205)	$	795	$	421	$	374
Ameren Missouri	(51)		41		(92)		(398)		(328)		(70)		316		272		44
Ameren Illinois	13		232		(219)		(337)		(323)		(14)		326		106		220

Cash Flows from Operating Activities

Our cash provided by operating activities is affected by fluctuations of trade accounts receivable, inventories, and accounts and wages payable, among other things, as well as the unique regulatory environment for each of our businesses. Substantially all expenditures related to fuel, purchased power, and natural gas purchased for resale are recovered from customers through rate adjustment mechanisms, which may be adjusted without a traditional rate proceeding. Similar regulatory mechanisms exist for certain other operating expenses that can also affect the timing of cash provided by operating activities. The timing of cash payments for costs recoverable under our regulatory mechanisms differs from the recovery period of those costs. Additionally, the seasonality of our electric and natural gas businesses, primarily caused by seasonal customer rates and changes in customer demand due to weather, significantly affects the amount and timing of our cash provided by operating activities.

Ameren

Ameren’s cash provided by operating activities decreased $325 million in the first three months of 2021, compared with the year-ago period. The following items contributed to the decrease:

•A $309 million decrease resulting from increased purchases in natural gas for resale and purchased power costs as a result of the significant increase in customer demand and prices for natural gas and electricity experienced in mid-February 2021 due to extremely cold weather, which are recovered under the PGA, FAC, and Ameren Illinois’ purchased power rider; a net decrease attributable to other regulatory recovery mechanisms; and a decrease in customer collections at Ameren Illinois, primarily due to an increase in accounts receivable balances, which reflected an increase in amounts that were 30 days or greater past due or that were a part of a deferred payment arrangement. These items were partially offset by increased customer collections resulting from base rate increases related to sales volumes and PISA at Ameren Missouri and increased natural gas revenues at Ameren Illinois as a result of the January 2021 rate order.

•A $26 million increase in interest payments, primarily due to an increase in the average outstanding debt at Ameren (parent) and Ameren Missouri.

•A $16 million increase in major storm restoration costs at Ameren Illinois due to a January 2021 storm.

•A $9 million increase in property tax payments at Ameren Missouri primarily due to higher assessed property tax values.

•A $7 million decrease in net collateral activity with counterparties, primarily resulting from changes in the market prices of power, natural gas, and other fuels.

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The following items partially offset the decrease in Ameren’s cash from operating activities between periods:

•A $35 million increase resulting from a decrease in coal inventory levels at Ameren Missouri due to increased consumption levels, compared with the year-ago period.

•An $11 million decrease in payments to settle ARO liabilities, primarily related to the closure of Ameren Missouri’s CCR storage facilities.

Ameren Missouri

Ameren Missouri’s cash provided by operating activities decreased $92 million in the first three months of 2021, compared with the year-ago period. The following items contributed to the decrease:

•A $111 million decrease resulting from increased purchases in natural gas for resale and purchased power costs as a result of the significant increase in customer demand and prices for natural gas and electricity experienced in mid-February 2021 due to extremely cold weather, which are recovered under the PGA and FAC and a net decrease attributable to other regulatory recovery mechanisms. These items were partially offset by increased customer collections resulting from base rate increases related to sales volumes and PISA.

•A $10 million increase in interest payments, primarily due to an increase in the average outstanding debt.

•A $9 million increase in property tax payments primarily due to higher assessed property tax values.

•An $8 million decrease in net collateral activity with counterparties, primarily resulting from changes in the market prices of power, natural gas, and other fuels.

The following items partially offset the decrease in Ameren Missouri’s cash from operating activities between periods:

•A $35 million increase resulting from a decrease in coal inventory levels due to increased consumption levels, compared with the year-ago period.

•An $11 million decrease in payments to settle ARO liabilities, primarily related to the closure of CCR storage facilities.

Ameren Illinois

Ameren Illinois’ cash provided by operating activities decreased $219 million in the first three months of 2021, compared with the year-ago period. The following items contributed to the decrease:

•A $202 million decrease resulting from increased purchases in natural gas for resale and purchased power costs as a result of the significant increase in customer demand and prices for natural gas and electricity experienced in mid-February 2021 due to extremely cold weather, which are recovered under the PGA and purchased power rider; a net decrease attributable to other regulatory recovery mechanisms; and a decrease in customer collections, primarily due to an increase in accounts receivable balances, which reflected an increase in amounts that were 30 days or greater past due or that were a part of a deferred payment arrangement. These items were partially offset by increased natural gas revenues as a result of the January 2021 rate order.

•A $16 million increase in major storm restoration costs due to a January 2021 storm.

Cash Flows from Investing Activities

Ameren’s cash used in investing activities increased $205 million during the first three months of 2021, compared with the year-ago period, primarily as a result of a $193 million increase in cash paid for the acquisition of wind generation assets and a $58 million increase in capital expenditures, which were driven by increases at Ameren Missouri and Ameren Illinois, partially offset by a decrease at ATXI primarily as a result of decreased Illinois Rivers transmission line expenditures, as it was placed in service in December 2020. The increase in Ameren’s cash used in investing activities was partially offset by a $34 million decrease due to the timing of nuclear fuel expenditures and a $13 million decrease due to net investment activity in the nuclear decommissioning trust fund at Ameren Missouri.

Ameren Missouri’s cash used in investing activities increased $70 million during the first three months of 2021, compared with the year-ago period, primarily as a result of a $193 million increase in cash paid for the acquisition of wind generation assets and a $63 million increase in capital expenditures, primarily related to electric delivery infrastructure upgrades, electric distribution system reliability projects, and generator repairs to the Callaway Energy Center. The increase in Ameren Missouri’s cash used in investing activities was partially offset by a $139 million decrease in net money pool advances, a $34 million decrease due to the timing of nuclear fuel expenditures, and a $13 million decrease due to net investment activity in the nuclear decommissioning trust fund.

Ameren Illinois’ cash used in investing activities increased $14 million during the first three months of 2021, compared with the year-ago period, due to an increase in capital expenditures, primarily related to software and communication network projects.

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Cash Flows from Financing Activities

Cash provided by, or used in, financing activities is a result of our financing needs, which depend on the level of cash provided by operating activities, the level of cash used in investing activities, the level of dividends, and our long-term debt maturities, among other things.

Ameren’s cash provided by consolidated financing activities increased $374 million during the first three months of 2021, compared with the year-ago period. During the first three months of 2021, Ameren utilized proceeds from the issuance of $450 million of long-term debt for general corporate purposes, including to repay then-outstanding short-term debt, and to fund, in part, investing activities. Ameren also utilized net proceeds from commercial paper issuances of $399 million and cash on hand to fund operating activities, including increased purchases in natural gas for resale and purchased power costs as a result of the significant increase in customer demand and prices for natural gas and electricity experienced in mid-February 2021 due to extremely cold weather, and to fund, in part, investing activities. In addition, Ameren received cash proceeds of $113 million from the settlement of the remaining portion of the forward sale agreement of common stock that were used to fund a portion of Ameren Missouri’s wind generation investments. In comparison, during the first three months of 2020, Ameren utilized proceeds of $640 million from a long-term debt issuance, credit facility borrowings, and net commercial paper issuances to repay at maturity long-term debt of $85 million and to fund, in part, investing activities. During the first three months of 2021, Ameren paid common stock dividends of $140 million, compared with $122 million in dividend payments in the year-ago period.

Ameren Missouri’s cash provided by financing activities increased $44 million during the first three months of 2021, compared to the year-ago period. During the first three months of 2021, Ameren Missouri utilized net proceeds from commercial paper issuances of $204 million and cash on hand to fund operating activities, including increased purchases in natural gas for resale and purchased power costs as a result of the significant increase in customer demand and prices for natural gas and electricity experienced in mid-February 2021 due to extremely cold weather, and to fund, in part, investing activities. Additionally, Ameren Missouri utilized a $113 million capital contribution from Ameren (parent) to fund, in part, its wind generation expenditures. In comparison, during the first three months of 2020, Ameren Missouri utilized net proceeds from the issuance of $465 million in long-term debt to repay then-outstanding commercial paper issuances, including short-term debt incurred in connection with the repayment at maturity of long-term debt of $85 million. In 2020, Ameren Missouri repaid net short-term debt of $104 million and used cash provided by financing activities to fund, in part, investing activities.

Ameren Illinois’ cash provided by financing activities increased $220 million during the first three months of 2021, compared with the year-ago period. During the first three months of 2021, Ameren Illinois utilized net proceeds from commercial paper issuances of $323 million to fund operating activities, including increased purchases in natural gas for resale and purchased power costs as a result of the significant increase in customer demand and prices for natural gas and electricity experienced in mid-February 2021 due to extremely cold weather, and to fund, in part, investing activities. Ameren Illinois received a $40 million capital contribution from Ameren (parent), the first three months of 2021, compared to a $100 million capital contribution in the year-ago period. In addition, Ameren Illinois repaid $19 million of money pool borrowings and redeemed $13 million of preferred stock in the current year period.

See Long-term Debt and Equity in this section for additional information on maturities and issuances of long-term debt, issuances of common stock, and redemptions of preferred stock.

Credit Facility Borrowings and Liquidity

The liquidity needs of the Ameren Companies are typically supported through the use of available cash, drawings under committed credit agreements, commercial paper issuances, and/or, in the case of Ameren Missouri and Ameren Illinois, short-term affiliate borrowings. See Note 3 – Short-term Debt and Liquidity under Part I, Item 1, of this report for additional information on credit agreements, commercial paper issuances, Ameren’s money pool arrangements and related borrowings, and relevant interest rates.

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The following table presents Ameren’s consolidated liquidity as of March 31, 2021:

Ameren (parent) and Ameren Missouri:
Missouri Credit Agreement – borrowing capacity	$	1,200
Less: Ameren (parent) commercial paper outstanding	233
Less: Ameren Missouri commercial paper outstanding	204
Less: Ameren Missouri letters of credit	3
Missouri Credit Agreement – subtotal	760
Ameren (parent) and Ameren Illinois:
Illinois Credit Agreement – borrowing capacity	1,100
Less: Ameren (parent) commercial paper outstanding	129
Less: Ameren Illinois commercial paper outstanding	323
Less: Ameren Illinois letters of credit	1
Illinois Credit Agreement – subtotal	647
Subtotal	$	1,407
Add: Cash and cash equivalents	6
Net Available Liquidity	$	1,413

The Credit Agreements, among other things, provide $2.3 billion of credit until maturity in December 2024. See Note 3 – Short-term Debt and Liquidity under Part I, Item 1, of this report for additional information on the Credit Agreements. During the three months ended March 31, 2021, Ameren (parent), Ameren Missouri, and Ameren Illinois each issued commercial paper. Borrowings under the Credit Agreements and commercial paper issuances are based upon available interest rates at that time of the borrowing or issuance.

Ameren has a money pool agreement with and among its utility subsidiaries to coordinate and to provide for certain short-term cash and working capital requirements. As short-term capital needs arise, and based on availability of funding sources, Ameren Missouri and Ameren Illinois will access funds from the utility money pool, the Credit Agreements, or the commercial paper programs depending on which option has the lowest interest rates.

The issuance of short-term debt securities by Ameren’s utility subsidiaries is subject to FERC approval under the Federal Power Act. In 2020, the FERC issued orders authorizing Ameren Missouri and Ameren Illinois to each issue up to $1 billion of short-term debt securities through March 2022 and September 2022, respectively. In July 2019, the FERC issued an order authorizing ATXI to issue up to $300 million of short-term debt securities, which expires in July 2021.

The Ameren Companies continually evaluate the adequacy and appropriateness of their liquidity arrangements for changing business conditions. When business conditions warrant, changes may be made to existing credit agreements or to other borrowing arrangements, or other arrangements may be made.

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Long-term Debt and Equity

The following table presents Ameren’s issuances (net of any issuance premiums or discounts) of long-term debt and equity, as well as maturities of long-term debt and redemptions of preferred stock for the three months ended March 31, 2021 and 2020:

	Month Issued, Redeemed, or Matured	2021		2020
Issuances of Long-term Debt
Ameren:
1.75% Senior unsecured notes due 2028	March	$	450	$	—
Ameren Missouri:
2.95% First mortgage bonds due 2030	March	$	—	$	465
Total Ameren long-term debt issuances		$	450	$	465
Issuances of Common Stock
Ameren:
DRPlus and 401(k) (a)	Various	$	12	$	13
Forward sale agreement (b)	February	113		—
Total common stock issuances (c)		$	125	$	13
Total Ameren long-term debt and common stock issuances		$	575	$	478
Maturities of Long-term Debt
Ameren Missouri:
5.00% Senior secured notes due 2020	February	$	—	$	85
Total Ameren long-term debt maturities		$	—	$	85
Redemptions of Preferred Stock
Ameren Illinois:
6.625% Series	March	$	12	$	—
7.75% Series	March	1		—
Total Ameren Illinois preferred stock redemptions		$	13	$	—
Total Ameren long-term debt maturities and preferred stock redemptions		$	13	$	85

(a)Ameren issued a total of 0.1 million and 0.2 million shares of common stock under its DRPlus and 401(k) plan in the three months ended March 31, 2021 and 2020, respectively.

(b)Ameren issued 1.6 million shares of common stock to settle the remainder of the forward sale agreement.

(c)Excludes 0.5 million and 0.5 million shares of common stock valued at $33 million and $38 million issued for no cash consideration in connection with stock-based compensation for the three months ended March 31, 2021 and 2020, respectively.

See Note 4 – Long-Term Debt and Equity Financings under Part I, Item 1, of this report for additional information, including proceeds from issuances of long-term debt, the use of those proceeds and Ameren’s forward equity sale agreement.

Indebtedness Provisions and Other Covenants

At March 31, 2021, the Ameren Companies were in compliance with the provisions and covenants contained in their credit agreements, indentures, and articles of incorporation, as applicable, and ATXI was in compliance with the provisions and covenants contained in its note purchase agreement. See Note 3 – Short-term Debt and Liquidity under Part I, Item 1, of this report and Note 4 – Short-term Debt and Liquidity and Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of the Form 10-K for a discussion of provisions (and applicable cross-default provisions) and covenants contained in our credit agreements, in ATXI’s note purchase agreement, and in certain of the Ameren Companies’ indentures and articles of incorporation.

We consider access to short-term and long-term capital markets to be a significant source of funding for capital requirements not satisfied by cash provided by our operating activities. Inability to raise capital on reasonable terms, particularly during times of uncertainty in the capital markets, could negatively affect our ability to maintain and expand our businesses. After assessing its current operating performance, liquidity, and credit ratings (see Credit Ratings below), Ameren, Ameren Missouri, and Ameren Illinois each believes that it will continue to have access to the capital markets on reasonable terms. However, events beyond Ameren’s, Ameren Missouri’s, and Ameren Illinois’ control may create uncertainty in the capital markets or make access to the capital markets uncertain or limited. Such events could increase our cost of capital and adversely affect our ability to access the capital markets.

Dividends

The amount and timing of dividends payable on Ameren’s common stock are within the sole discretion of Ameren’s board of directors. Ameren’s board of directors has not set specific targets or payout parameters when declaring common stock dividends, but it considers various factors, including Ameren’s overall payout ratio, payout ratios of our peers, projected cash flow and potential future cash flow requirements, historical earnings and cash flow, projected earnings, impacts of regulatory orders or legislation, and other key business

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considerations. Ameren expects its dividend payout ratio to be between 55% and 70% of annual earnings over the next few years. On May 7, 2021, Ameren’s board of directors declared a quarterly common stock dividend of 55 cents per share payable on June 30, 2021, to shareholders of record on June 9, 2021.

See Note 4 – Short-term Debt and Liquidity and Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of the Form 10-K for additional discussion of covenants and provisions contained in certain of the Ameren Companies’ financial agreements and articles of incorporation that would restrict the Ameren Companies’ payment of dividends in certain circumstances. At March 31, 2021, none of these circumstances existed at Ameren, Ameren Missouri, or Ameren Illinois and, as a result, these companies were not restricted from paying dividends.

The following table presents common stock dividends declared and paid by Ameren Corporation to its common shareholders and by Ameren subsidiaries to their parent, Ameren Corporation, for the three months ended March 31, 2021 and 2020:

	Three Months
	2021		2020
Ameren	$	140	$	122
ATXI	25		—

Commitments

As of March 31, 2021, there have been no material changes other than in the ordinary course of business related to cash requirements arising from contractual obligations provided in Item 7 of the Form 10-K for the year ended December 31, 2020, with the exception of Ameren parent’s debt issuance discussed in Long-Term Debt and Equity section above.

Off-balance-sheet Arrangements

At March 31, 2021, none of the Ameren Companies had any significant off-balance-sheet financing arrangements, other than variable interest entities. See Note 1 – Summary of Significant Accounting Policies under Part I, Item 1, of this report for further detail concerning variable interest entities.

Credit Ratings

Our credit ratings affect our liquidity, our access to the capital markets and credit markets, our cost of borrowing under our credit facilities and our commercial paper programs, and our collateral posting requirements under commodity contracts.

The following table presents the principal credit ratings by Moody’s and S&P, as applicable, effective on the date of this report:

	Moody’s	S&P
Ameren:
Issuer/corporate credit rating	Baa1	BBB+
Senior unsecured debt	Baa1	BBB
Commercial paper	P-2	A-2
Ameren Missouri:
Issuer/corporate credit rating	Baa1	BBB+
Secured debt	A2	A
Senior unsecured debt	Baa1	Not Rated
Commercial paper	P-2	A-2
Ameren Illinois:
Issuer/corporate credit rating	A3	BBB+
Secured debt	A1	A
Senior unsecured debt	A3	BBB+
Commercial paper	P-2	A-2
ATXI:
Issuer credit rating	A2	Not Rated
Senior unsecured debt	A2	Not Rated

A credit rating is not a recommendation to buy, sell, or hold securities. It should be evaluated independently of any other rating. Ratings are subject to revision or withdrawal at any time by the rating organization.

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Collateral Postings

Any weakening of our credit ratings may reduce access to capital and trigger additional collateral postings and prepayments. Such changes may also increase the cost of borrowing, resulting in an adverse effect on earnings. Cash collateral postings and prepayments made with external parties, including postings related to exchange-traded contracts, and cash collateral posted by external parties were immaterial at March 31, 2021. A sub-investment-grade issuer or senior unsecured debt rating (below “Baa3” from Moody’s or below “BBB-” from S&P) at March 31, 2021, could have resulted in Ameren, Ameren Missouri, or Ameren Illinois being required to post additional collateral or other assurances for certain trade obligations amounting to $117 million, $104 million, and $13 million, respectively.

Changes in commodity prices could trigger additional collateral postings and prepayments. Based on credit ratings at March 31, 2021, if market prices were 15% higher or lower than March 31, 2021 levels in the next 12 months and 20% higher or lower thereafter through the end of the term of the commodity contracts, then Ameren, Ameren Missouri, or Ameren Illinois could be required to post an immaterial amount, compared to each company’s liquidity, of collateral or other assurances for certain trade obligations.

OUTLOOK

Below are some key trends, events, and uncertainties that may reasonably affect our results of operations, financial condition, or liquidity, as well as our ability to achieve strategic and financial objectives, for 2021 and beyond. The continued effect of the COVID-19 pandemic on our results of operations, financial position, and liquidity in subsequent periods will depend on its severity and longevity, future regulatory or legislative actions with respect thereto, and the resulting impact on business, economic, and capital market conditions. We continue to assess the impacts the COVID-19 pandemic is having on our businesses, including but not limited to impacts on our liquidity; demand for residential, commercial, and industrial electric and natural gas services; changes in deferred payment arrangements for customers; the timing and extent to which recovery of incremental costs incurred, net of savings, and forgone customer late fee revenues at Ameren Missouri is allowed by the MoPSC; changes in our ability to disconnect customers for nonpayment; bad debt expense; supply chain operations; the availability of our employees and contractors; counterparty credit; capital construction; infrastructure operations and maintenance; energy-efficiency programs; and pension valuations. For additional information regarding recent rate orders, lawsuits, and pending requests filed with state and federal regulatory commissions, including those discussed below, see Note 2 – Rate and Regulatory Matters under Part I, Item 1, of this report and Note 2 – Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K.

Operations

•In the first three months of 2021, our sales volumes, which have been, and continue to be, affected by the COVID-19 pandemic, among other things, were comparable to the same period in 2020, excluding the estimated effects of weather and customer energy efficiency programs. We expect a gradual improvement in sales volumes in 2021, compared to 2020. Our customers’ payment for services has been adversely affected by the COVID-19 pandemic, which led to an increase in our accounts receivable balances that are past due or that are a part of a deferred payment arrangement. Because of their regulatory frameworks, Ameren Illinois’ and ATXI’s revenues are largely decoupled from changes in sales volumes. See the Results of Operations section above for additional information on our accounts receivable balances, Ameren Illinois’ electric and natural gas bad debt riders, and changes in Ameren Missouri’s sales volumes in the first three months of 2021, compared to the same period in 2020, and sales volumes expected in 2021, compared to 2020. Additionally, see Note 2 – Rate and Regulatory Matters under Part I, Item 1, of this report and Note 2 – Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K for information on Ameren Missouri’s and Ameren Illinois’ reinstatement of customer disconnection and late fee charges for non-payment, accounting authority orders issued by the MoPSC related to Ameren Missouri's electric and natural gas services to allow Ameren Missouri to accumulate certain costs incurred, net of savings, and forgone customer late fee revenues related to the COVID-19 pandemic for consideration of recovery in the current electric and natural gas service regulatory rate reviews, and orders issued by the ICC in a service disconnection moratorium proceeding, which required Ameren Illinois to implement more flexible credit and collection practices and allowed for recovery of costs incurred related to the COVID-19 pandemic and forgone late fees.

•The PISA permits Ameren Missouri to defer and recover 85% of the depreciation expense and earn a return at the applicable WACC on investments in certain property, plant, and equipment placed in service, and not included in base rates. The regulatory asset for accumulated PISA deferrals also earns a return at the applicable WACC, with all approved PISA deferrals added to rate base prospectively and recovered over a period of 20 years following a regulatory rate review. Additionally, under the RESRAM, Ameren Missouri is permitted to recover the 15% of depreciation expense not recovered under the PISA, and earn a return at the applicable WACC for investments in renewable generation plant placed in service. Accumulated RESRAM deferrals earn carrying costs at short-term interest rates. The PISA and the RESRAM mitigate the effects of regulatory lag between regulatory rate reviews. Those investments not eligible for recovery under the PISA and the remaining 15% of certain property, plant, and equipment placed in service, unless eligible for recovery under the RESRAM, remain subject to regulatory lag. Ameren Missouri recognizes the cost of debt on PISA deferrals in revenue, instead of using the applicable WACC, with the difference recognized in revenues when recovery of such deferrals is reflected in customer rates. As a result of the PISA election, additional provisions of the law apply to Ameren Missouri, including

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limitations on electric customer rate increases. Ameren Missouri does not expect to exceed these rate increase limitations in 2021. Both the rate increase limitation and the PISA are effective through December 2023, unless Ameren Missouri requests and the MoPSC approves an extension through December 2028.

•In 2018, the MoPSC issued an order approving Ameren Missouri’s MEEIA 2019 plan. The plan includes a portfolio of customer energy-efficiency programs through December 2022 and low-income customer energy-efficiency programs through December 2024, along with a rider. Ameren Missouri intends to invest $290 million over the life of the plan, including $65 million in 2021 and $70 million in 2022. The plan includes the continued use of the MEEIA rider, which allows Ameren Missouri to collect from, or refund to, customers any difference in actual MEEIA program costs and related lost electric margins and the amounts collected from customers. In addition, the plan includes a performance incentive that provides Ameren Missouri an opportunity to earn additional revenues by achieving certain customer energy-efficiency goals. If the target goals were achieved for 2020, additional revenues of $10 million would be recognized in 2021, and, if target goals are achieved for 2021 and 2022, additional revenues of $24 million would be recognized in 2022. Incremental additional revenues of $3 million, $3 million, and $1 million may be earned for 2020, 2021, and 2022, respectively, and would be recognized in the respective following year if Ameren Missouri exceeds its targeted goals. Ameren Missouri’s ability to achieve and/or exceed targeted goals could be affected by the COVID-19 pandemic. For the year ended December 31, 2020, Ameren Missouri recognized $6 million in revenues related to MEEIA performance incentives.

•In March 2021, Ameren Missouri filed a request with the MoPSC seeking approval to increase its annual revenues for electric service by $299 million. The MoPSC proceeding relating to the proposed electric service rate changes will take place over a period of up to 11 months, with a decision by the MoPSC expected by February 2022 and new rates effective by March 2022. Ameren Missouri cannot predict the level of any electric service rate change the MoPSC may approve, or whether any rate change that may eventually be approved will be sufficient for Ameren Missouri to recover its costs and earn a reasonable return on its investments when the rate change goes into effect.

•In March 2020, the MoPSC issued an order in Ameren Missouri’s July 2019 electric service regulatory rate review, resulting in a decrease of $32 million to Ameren Missouri’s annual revenue requirement for electric retail service. The order also approved a change in rate design, which will result in winter rates applied to May usage and summer rates applied to September usage beginning in 2021. Previously, blended rates were applied to both months’ usage. The quarterly year-over-year increases/(decreases) to 2021 earnings, compared to the same periods in 2020, from the effect of the change in rate design are estimated at approximately ($50) million and $50 million for the second and third quarter comparisons, respectively.

•Ameren Illinois and ATXI use a forward-looking rate calculation with an annual revenue requirement reconciliation for each company’s electric transmission business. Based on expected rate base growth and the currently allowed 10.52% ROE, which includes a 50 basis point adder for participation in an RTO, the revenue requirements included in 2021 rates for Ameren Illinois’ and ATXI’s electric transmission businesses are $380 million and $200 million, respectively. These revenue requirements represent an increase in Ameren Illinois’ and ATXI’s revenue requirements of $67 million and $8 million, respectively, from the revenue requirements reflected in 2020 rates, primarily due to expected rate base growth. These rates will affect Ameren Illinois’ and ATXI’s cash receipts during 2021, but will not determine their respective electric transmission service operating revenues, which will instead be based on 2021 actual recoverable costs, rate base, and a return on rate base at the applicable WACC as calculated under the FERC formula ratemaking framework.

•The allowed base ROE for FERC-regulated transmission rates previously charged under the MISO tariff is the subject of an appeal filed with the United States Court of Appeals for the District of Columbia Circuit. Depending on the outcome of the appeal, the transmission rates charged during previous periods and the currently effective rates may be subject to change. Additionally, in March 2019, the FERC issued a Notice of Inquiry regarding its transmission incentives policy. In March 2020, the FERC issued a Notice of Proposed Rulemaking on its transmission incentives policy, which addressed many of the issues in the Notice of Inquiry on transmission incentives. The Notice of Proposed Rulemaking included an increased incentive in the allowed base ROE for participation in an RTO to 100 basis points from the current 50 basis points and revised the parameters for awarding incentives, while limiting the overall incentives to a cap of 250 basis points, among other things. In April 2021, the FERC issued a Supplemental Notice of Proposed Rulemaking, which proposes to modify the Notice of Proposed Rulemaking’s incentive for participation in an RTO by limiting this incentive for utilities that join an RTO to 50 basis points and only allowing them to earn the incentive for three years, among other things. If this proposal is included in a final rule, Ameren Illinois and ATXI would no longer be eligible for the 50 basis point RTO incentive adder, prospectively. The FERC is under no deadline to issue a final rule on this matter. Ameren is unable to predict the ultimate impact of any changes to the FERC’s incentives policy, or any further order on base ROE. A 50 basis point change in the FERC-allowed base ROE would affect Ameren’s and Ameren Illinois’ annual net income by an estimated $11 million and $7 million, respectively, based on each company’s 2021 projected rate base.

•Ameren Illinois’ electric distribution service performance-based formula ratemaking framework allows Ameren Illinois to reconcile electric distribution service rates to its actual revenue requirement on an annual basis. If a given year’s revenue requirement varies from the amount collected from customers, an adjustment is made to electric operating revenues with an offset to a regulatory asset or liability to

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reflect that year’s actual revenue requirement, independent of actual sales volumes. The regulatory balance is then collected from, or refunded to, customers within two years from the end of the year. Unless extended by legislation, the ability to conduct annual updates to performance-based formula rates expires at the end of 2022. If not extended, Ameren Illinois would be required to establish future rates through a traditional regulatory rate review with the ICC, which would allow the use of a future test year. The decoupling provisions extend beyond the end of 2022 by law, which ensures that Ameren Illinois’ electric distribution revenues authorized in a regulatory rate review are not affected by changes in sales volumes. Ameren Illinois is actively pursuing constructive ratemaking. In March 2021, the ICC issued an order approving Ameren Illinois’ requested tariff to reconcile its electric distribution service revenue requirement for a period of up to two years after the final customer rate update under performance-based formula ratemaking. To utilize the reconciliation, the ICC-approved tariff requires Ameren Illinois to file a traditional regulatory rate review for its electric distribution service, which may be based on a future test year, by the end of March in the year following the last year in which an annual performance-based formula rate update was permitted.

•In 2020, the ICC issued an order in Ameren Illinois’ annual update filing that approved a $49 million decrease in Ameren Illinois’ electric distribution service rates beginning in January 2021. Illinois law provides for an annual reconciliation of the electric distribution revenue requirement as is necessary to reflect the actual costs incurred and a return at the applicable WACC on year-end rate base in a given year with the revenue requirement that was reflected in customer rates for that year. Consequently, Ameren Illinois’ 2021 electric distribution service revenues will be based on its 2021 actual recoverable costs, 2021 year-end rate base, and a return at the applicable WACC, with the ROE based on the annual average of the monthly yields of the 30-year United States Treasury bonds plus 580 basis points. As of March 31, 2021, Ameren Illinois expects its 2021 electric distribution year-end rate base to be $3.7 billion. With or without extension of the formula ratemaking framework, the 2021 revenue requirement reconciliation will be collected from, or refunded to, customers in 2023. A 50 basis point change in the annual average of the monthly yields of the 30-year United States Treasury bonds would result in an estimated $10 million change in Ameren’s and Ameren Illinois’ annual net income, based on Ameren Illinois’ 2021 projected year-end rate base, including electric energy-efficiency investments. Ameren Illinois’ allowed ROE for the first three months of 2021 was based on an estimated annual average of the monthly yields of the 30-year United States Treasury bonds of 2.37%.

•In April 2021, Ameren Illinois filed its annual electric distribution service performance-based formula rate update with the ICC, requesting an increase of $64 million in its rates. An ICC decision in this proceeding is expected by December 2021, with new rates effective January 2022. These rates will affect Ameren Illinois' cash receipts during 2022, but will not affect electric distribution service revenues, which will be based on 2022 actual recoverable costs, 2022 year-end rate base, and a return at the applicable WACC as calculated under the Illinois performance-based formula ratemaking framework.

•In January 2021, the ICC issued an order in Ameren Illinois’ February 2020 natural gas delivery service regulatory rate review, which resulted in an increase to its annual revenues for natural gas delivery service of $76 million. The new rates became effective in January 2021. As a result of this order, the rate base under the QIP was reset to zero. Ameren Illinois used a 2021 future test year in this proceeding. The order also approved the implementation of a change in rate design, which concentrates more revenues in the winter heating season due to an increase in volumetric rates and a decrease in fixed customer rates. As such, the change in rate design will have an impact on interim period 2021 earnings, compared to 2020, but is not expected to materially affect annual earnings comparisons. The quarterly year-over-year increases/(decreases) to 2021 earnings, compared to the same periods in 2020, from the combined effect of the rate increase and the change in rate design are estimated at $17 million, ($7) million, and $7 million for the first quarter, third quarter, and fourth quarter comparisons, respectively.

•Pursuant to Illinois law, Ameren Illinois’ electric energy-efficiency investments are deferred as a regulatory asset and earn a return at the applicable WACC, with the ROE based on the annual average of the monthly yields of the 30-year United States Treasury bonds plus 580 basis points. The allowed ROE on electric energy-efficiency investments can be increased or decreased by up to 200 basis points, depending on the achievement of annual energy savings goals. Ameren Illinois plans to invest up to approximately $100 million per year in electric energy-efficiency programs through 2025. While the ICC has approved a plan consistent with this spending level through 2021, the ICC has the ability to reduce the amount of electric energy-efficiency savings goals in future plan program years if there are insufficient cost-effective programs available, which could reduce the investments in electric energy-efficiency programs. The electric energy-efficiency program investments and the return on those investments are collected from customers through a rider and are not included in the electric distribution service performance-based formula ratemaking framework. In March 2021, Ameren Illinois filed with the ICC an energy-efficiency plan which includes annual investments in electric energy-efficiency programs up to approximately $100 million per year from 2022 through 2025. A decision by the ICC in this proceeding is expected by September 2021.

•During its return to full power after the completion of the last refueling and maintenance outage in late December 2020, the Callaway Energy Center experienced a non-nuclear operating issue related to its generator. A thorough investigation of this matter was conducted. Work continues to replace certain key components of the generator in order to return the energy center to service. Ameren Missouri expects generator repairs of approximately $65 million, which are expected to be largely capital expenditures. Due to the long lead time for the manufacture, repair, and installation of the components, the energy center is expected to return to service in July 2021. In April 2021, Ameren Missouri’s insurance claims were accepted by NEIL, which are expected to cover a significant portion of the

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capital expenditures and replacement power costs. Replacement power costs of up to $4.5 million weekly are covered by insurance after March 17, 2021. Insurance recoveries related to replacement power costs will be reflected in electric operating revenues and included in net energy costs under the FAC. Insurance recoveries related to the capital expenditures will be reflected as a reduction to property, plant, and equipment. For the duration of the unplanned outage, Ameren Missouri expects an increase to its purchased power expense and a decrease to its off-system sales, with changes to both items recovered through the FAC. Ameren Missouri does not expect a significant increase to other operations and maintenance expense as a result of the unplanned outage. Pursuant to a February 2020 MoPSC order, Ameren Missouri deferred, as a regulatory asset, a total of $39 million in maintenance expenses related to its scheduled fall 2020 outage, which it began to amortize in January 2021. The regulatory asset will be amortized until the completion of the next refueling and maintenance outage, which is scheduled for the spring of 2022.

•Ameren Missouri and Ameren Illinois continue to make infrastructure investments and expect to seek increases to electric and natural gas rates to recover the cost of investments and earn an adequate return. Ameren Missouri and Ameren Illinois will also seek new, or to maintain existing, legislative solutions to address regulatory lag and to support investment in their utility infrastructure for the benefit of their customers. Ameren Missouri and Ameren Illinois continue to face cost recovery pressures, including limited economic growth in their service territories, economic impacts of the COVID-19 pandemic, customer conservation efforts, the impacts of additional customer energy-efficiency programs, and increased customer use of increasingly cost-effective technological advances, including private generation and energy storage. However, over the long-term, we expect the decreased demand to be partially offset by increased demand resulting from increased electrification of the economy for efficiencies and as a means to address economy-wide CO2 emission concerns. We expect that increased investments, including expected future investments for environmental compliance, system reliability improvements, and potential new generation sources, will result in rate base and revenue growth but also higher depreciation and financing costs.

Liquidity and Capital Resources

•Our customers’ payment for our services has been adversely affected by the COVID-19 pandemic, resulting in a decrease to our cash flow from operations. See the Results of Operations section above for additional information on our accounts receivable balances. Further, our liquidity and our capital expenditure plans could be adversely affected by other impacts resulting from the COVID-19 pandemic, including but not limited to potential impacts on our ability to access the capital markets on reasonable terms and when needed, Ameren Missouri’s expected wind generation additions remaining in 2021, and the timing of tax payments and the utilization of tax credits. We expect to make significant capital expenditures to improve our electric and natural gas utility infrastructure, however, disruptions to the capital markets and the ability of our suppliers and contractors to perform as required under their contracts could impact the execution of our capital investment strategy. For further discussion on the impacts to our ability to access the capital markets and Ameren Missouri’s expected wind generation additions remaining in 2021, see below.

•In February 2021, Ameren Missouri filed an update to its Smart Energy Plan with the MoPSC, which includes a five-year capital investment overview with a detailed one-year plan for 2021. The plan is designed to upgrade Ameren Missouri’s electric infrastructure and includes investments that will upgrade the grid and accommodate more renewable energy. Investments under the plan are expected to total approximately $8.4 billion over the five-year period from 2021 through 2025, with expenditures largely recoverable under the PISA and the RESRAM. The planned investments in 2024 and 2025 are based on the assumption that Ameren Missouri requests and receives MoPSC approval of an extension of the PISA through December 2028.

•In connection with Ameren Missouri’s 2020 IRP, Ameren established a goal of achieving net-zero carbon emissions by 2050. Ameren is also targeting a 50% CO2 emission reduction by 2030 and an 85% reduction by 2040 from the 2005 level. The plan, which is subject to review by the MoPSC for compliance with Missouri law, targets cleaner and more diverse sources of energy generation, including solar, wind, hydro, and nuclear power, and supports increased investment in new energy technologies. It also includes expanding renewable sources by adding 3,100 MWs of renewable generation by the end of 2030 and a total of 5,400 MWs of renewable generation by 2040. These amounts include 700 MWs related to the High Prairie and Atchison renewable energy centers, which will support Ameren Missouri’s compliance with the state of Missouri’s requirement of achieving 15% of native load sales from renewable energy sources beginning in 2021. The plan also includes advancing the retirement dates of the Sioux and Rush Island coal-fired energy centers to 2028 and 2039, respectively, which are subject to the approval of a change in the assets’ depreciable lives by the MoPSC in Ameren Missouri’s current electric service regulatory rate review, the continued implementation of customer energy-efficiency programs, and the expectation that Ameren Missouri will seek NRC approval for an extension of the operating license for the Callaway Energy Center beyond its current 2044 expiration date. Additionally, the plan includes retiring the Meramec and Labadie coal-fired energy centers at the end of their useful lives (by 2022 and 2042, respectively). Ameren Missouri’s plan could be affected by, among other factors: Ameren Missouri’s ability to obtain a certificate of convenience and necessity from the MoPSC, and any other required approvals for the addition of renewable resources, retirement of energy centers, and new or continued customer energy-efficiency programs; the ability of developers to meet contractual commitments and timely complete projects, which is dependent upon the availability of necessary materials and equipment, including those that are affected by the disruptions in the global supply chain caused by the COVID-19 pandemic, among other things; the availability of federal production and investment tax credits related to renewable energy and Ameren

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Missouri’s ability to use such credits; the cost of wind, solar, and other renewable generation and storage technologies; changes in environmental regulations, including those related to carbon emissions; energy prices and demand; and Ameren Missouri’s ability to obtain timely interconnection agreements with the MISO or other RTOs at an acceptable cost. The next integrated resource plan is expected to be filed in September 2023.

•In January 2021, Ameren Missouri acquired an up-to 300-MW wind generation project located in northwestern Missouri and partially placed it in service as the Atchison Renewable Energy Center. As of the date of this filing, Ameren Missouri has placed approximately half of the project in service, representing a purchase price of approximately $250 million, including an immaterial amount of transaction costs. Ameren Missouri expects the remaining MWs of the project to be in service by the end of September 2021.

•Through 2025, we expect to make significant capital expenditures to improve our electric and natural gas utility infrastructure, with a major portion directed to our transmission and distribution systems. We estimate that we will invest up to $17.8 billion (Ameren Missouri – up to $9.3 billion; Ameren Illinois – up to $8.2 billion; ATXI – up to $0.2 billion) of capital expenditures during the period from 2021 through 2025. Ameren’s and Ameren Missouri’s estimates include 300 MWs of wind generation at the Atchison Renewable Energy Center, but exclude incremental renewable generation investment opportunities of 1,200 MWs by 2025, which are included in Ameren Missouri’s 2020 IRP. As of the date of this filing, no contractual agreements have been entered into, and no regulatory approvals have been requested, related to these opportunities. These planned investments are based on the assumption of continued constructive regulatory frameworks, including an assumption that Ameren Missouri requests and receives MoPSC approval of an extension of the PISA through December 2028.

•Environmental regulations, including those related to CO2 emissions, or other actions taken by the EPA or state regulators, or requirements that may result from the NSR and Clean Air Act Litigation discussed in Note 9 – Commitments and Contingencies under Part I, Item 1, of this report, could result in significant increases in capital expenditures and operating costs. Regulations enacted by a prior federal administration can be reviewed and repealed by the EPA, and replacement or alternative regulations can be proposed or adopted by the current federal administration, the EPA and state regulators. The ultimate implementation of any of these regulations, as well as the timing of any such implementation, is uncertain. However, the individual or combined effects of existing and new environmental regulations could result in significant capital expenditures, increased operating costs, or the closure or alteration of some of Ameren Missouri’s coal-fired energy centers. Ameren Missouri’s capital expenditures are subject to MoPSC prudence reviews, which could result in cost disallowances as well as regulatory lag. The cost of Ameren Illinois’ purchased power and natural gas purchased for resale could increase. However, Ameren Illinois expects that these costs would be recovered from customers with no material adverse effect on its results of operations, financial position, or liquidity. Ameren’s and Ameren Missouri’s earnings could benefit from increased investment to comply with environmental regulations if those investments are reflected and recovered on a timely basis in customer rates.

•The Ameren Companies have multiyear credit agreements that cumulatively provide $2.3 billion of credit through December 2024, subject to a 364-day repayment term for Ameren Missouri and Ameren Illinois, with the option to seek incremental commitments to increase the cumulative credit provided to $2.7 billion. See Note 3 – Short-term Debt and Liquidity under Part I, Item 1, of this report and Note 4 – Short-term Debt and Liquidity under Part II, Item 8, in the Form 10-K for additional information regarding the Credit Agreements. The Ameren Companies have no material maturities of long-term debt until 2022. Ameren Missouri and Ameren Illinois expect to issue long-term debt in 2021 and to use the proceeds for general corporate purposes, including to repay short-term debt. With the recently completed Ameren (parent) debt issuance and availability under the Credit Agreements, as well as the proceeds from the recent settlement of the forward sale agreement, Ameren, Ameren Missouri, and Ameren Illinois believe that their liquidity is adequate given their expected operating cash flows, capital expenditures, including expected wind generation additions remaining in 2021, and financing plans. The Ameren Companies continue to monitor the effect of the COVID-19 pandemic on their liquidity, including as a result of decreased sales and increased customer nonpayment. To date, the Ameren Companies have been able to access the capital markets on reasonable terms when needed. However, there can be no assurance that significant changes in economic conditions, disruptions in the capital and credit markets, or other unforeseen events will not materially affect their ability to execute their expected operating, capital, or financing plans.

•Ameren expects its cash used for currently planned capital expenditures and dividends to exceed cash provided by operating activities over the next several years. As part of its plan to fund the cash requirements for capital expenditures, Ameren is using newly issued shares of common stock, rather than market-purchased shares, to satisfy requirements under the DRPlus and employee benefit plans and expects to continue to do so through at least 2025. Ameren expects these issuances to provide equity of about $100 million annually. In addition to the issuance of common shares in connection with the 2021 settlement of the remaining portion of the forward sale agreement, Ameren plans to issue incremental equity of about $150 million in 2021 and about $300 million each year from 2022 to 2025. Ameren expects to establish an at-the-market equity program that will allow Ameren to meet equity needs through 2023, subject to market conditions and other factors. Ameren expects its equity to total capitalization to be about 45% through December 31, 2025, with the long-term intent to support solid investment-grade credit ratings. Ameren Missouri and Ameren Illinois expect to fund cash flow needs through debt issuances, adjustments of dividends to Ameren (parent), and/or capital contributions from Ameren (parent).

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•As of March 31, 2021, Ameren had $95 million in tax benefits from federal and state income tax credit carryforwards, $107 million in tax benefits from federal and state net operating loss carryforwards, and $12 million in tax benefits from federal and state income tax overpayments and outstanding refunds, which will be utilized in future periods. Ameren expects federal income tax payments at the required minimum levels from 2021 to 2025 resulting from the anticipated use of production tax credits that will be generated by Ameren Missouri’s High Prairie and Atchison renewable energy centers, existing tax net operating losses, tax credit carryforwards, and tax overpayments and outstanding refunds.

•As a result of the significant increase in customer demand and prices for natural gas and electricity experienced in mid-February 2021 due to extremely cold weather, for the month of February 2021, Ameren Missouri and Ameren Illinois had under-recovered commodity costs (Ameren Missouri - PGA $53 million, FAC $50 million; Ameren Illinois - PGA $221 million). Ameren Missouri’s PGA and FAC under-recoveries are designed to be collected from customers over 12 months beginning November 2021 and eight months beginning October 2021, respectively. Longer recovery periods may be sought by Ameren Missouri or imposed by the MoPSC to lessen the impact on customer rates. Ameren Illinois’ PGA under-recovery is being collected from customers over 12 months beginning April 2021, but the collection period may be extended at Ameren Illinois’ election to lessen the impact on customer rates.

The above items could have a material impact on our results of operations, financial position, and liquidity. Additionally, in the ordinary course of business, we evaluate strategies to enhance our results of operations, financial position, and liquidity. These strategies may include acquisitions, divestitures, opportunities to reduce costs or increase revenues, and other strategic initiatives to increase Ameren’s shareholder value. We are unable to predict which, if any, of these initiatives will be executed. The execution of these initiatives may have a material impact on our future results of operations, financial position, or liquidity.

REGULATORY MATTERS

See Note 2 – Rate and Regulatory Matters under Part I, Item 1, of this report.

ITEM 3. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK.

There have been no material changes to the quantitative and qualitative disclosures about interest rate risk, credit risk, investment price risk, commodity price risk, and commodity supplier risk included in the Form 10-K. See Item 7A under Part II of the Form 10-K for a more detailed discussion of our market risk.

ITEM 4. CONTROLS AND PROCEDURES.

(a)Evaluation of Disclosure Controls and Procedures

As of March 31, 2021, evaluations were performed under the supervision and with the participation of management, including the principal executive officer and the principal financial officer of each of the Ameren Companies, of the effectiveness of the design and operation of such registrant’s disclosure controls and procedures (as defined in Rules 13a-15(e) and 15d-15(e) of the Exchange Act). Based on those evaluations, as of March 31, 2021, the principal executive officer and the principal financial officer of each of the Ameren Companies concluded that such disclosure controls and procedures are effective to provide assurance that information required to be disclosed in such registrant’s reports filed or submitted under the Exchange Act is recorded, processed, summarized, and reported within the time periods specified in the SEC’s rules and forms and such information is accumulated and communicated to its management, including its principal executive officer and its principal financial officer, to allow timely decisions regarding required disclosure.

(b)Changes in Internal Controls over Financial Reporting

There has been no change in any of the Ameren Companies’ internal control over financial reporting during their most recent fiscal quarter that has materially affected, or is reasonably likely to materially affect, each of their internal control over financial reporting.

PART II. OTHER INFORMATION

ITEM 1. LEGAL PROCEEDINGS.

We are involved in legal and administrative proceedings before various courts and agencies with respect to matters that arise in the ordinary course of business, some of which involve substantial amounts of money. We believe that the final disposition of these proceedings, except as otherwise disclosed in this report, will not have a material adverse effect on our results of operations, financial position, or liquidity. Risk of loss is mitigated, in some cases, by insurance or contractual or statutory indemnification. We believe that we have established appropriate reserves for potential losses. For additional information on material legal and administrative proceedings, see Note 2 – Rate and Regulatory Matters, Note 9 – Commitments and Contingencies, and Note 10 – Callaway Energy Center, under Part I, Item 1, of this report. Pursuant to Item 103(c)(3)(iii) of Regulation S-K, our policy is to disclose environmental proceedings to which a governmental entity is a party if we reasonably believe such proceedings will result in monetary sanctions of $1 million or more.

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ITEM 1A. RISK FACTORS.

There have been no material changes to the risk factors disclosed in Part I, Item 1A, Risk Factors in the Form 10-K.

ITEM 2. UNREGISTERED SALES OF EQUITY SECURITIES AND USE OF PROCEEDS.

Ameren Corporation, Ameren Missouri, and Ameren Illinois did not purchase equity securities reportable under Item 703 of Regulation S-K during the period from January 1, 2021, to March 31, 2021.

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ITEM 6. EXHIBITS.

The documents listed below are being filed or have previously been filed on behalf of the Ameren Companies and are incorporated herein by reference from the documents indicated and made a part hereof. Exhibits not identified as previously filed are filed herewith.

Exhibit Designation	Registrant(s)	Nature of Exhibit	Previously Filed as Exhibit to:
Instruments Defining Rights of Security Holders, Including Indentures
4.1	Ameren	Ameren Indenture Company Order, dated March 5, 2021, establishing the 1.75% Senior Notes due 2028 (including the global note)	March 5, 2021 Form 8-K, Exhibits 4.3 and 4.4, File No. 1-14756
Rule 13a-14(a) / 15d-14(a) Certifications
31.1	Ameren	Rule 13a-14(a)/15d-14(a) Certification of Principal Executive Officer of Ameren
31.2	Ameren	Rule 13a-14(a)/15d-14(a) Certification of Principal Financial Officer of Ameren
31.3	Ameren Missouri	Rule 13a-14(a)/15d-14(a) Certification of Principal Executive Officer of Ameren Missouri
31.4	Ameren Missouri	Rule 13a-14(a)/15d-14(a) Certification of Principal Financial Officer of Ameren Missouri
31.5	Ameren Illinois	Rule 13a-14(a)/15d-14(a) Certification of Principal Executive Officer of Ameren Illinois
31.6	Ameren Illinois	Rule 13a-14(a)/15d-14(a) Certification of Principal Financial Officer of Ameren Illinois
Section 1350 Certifications
32.1	Ameren	Section 1350 Certification of Principal Executive Officer and Principal Financial Officer of Ameren
32.2	Ameren Missouri	Section 1350 Certification of Principal Executive Officer and Principal Financial Officer of Ameren Missouri
32.3	Ameren Illinois	Section 1350 Certification of Principal Executive Officer and Principal Financial Officer of Ameren Illinois
Interactive Data Files
101.INS	Ameren Companies	Inline XBRL Instance Document - the instance document does not appear in the Interactive Data File because its XBRL tags are embedded within the Inline XBRL document
101.SCH	Ameren Companies	Inline XBRL Taxonomy Extension Schema Document
101.CAL	Ameren Companies	Inline XBRL Taxonomy Extension Calculation Linkbase Document
101.LAB	Ameren Companies	Inline XBRL Taxonomy Extension Label Linkbase Document
101.PRE	Ameren Companies	Inline XBRL Taxonomy Extension Presentation Linkbase Document
101.DEF	Ameren Companies	Inline XBRL Taxonomy Extension Definition Document
104	Ameren Companies	Cover Page Interactive Data File (formatted as Inline XBRL and contained in Exhibit 101)

The file number references for the Ameren Companies’ filings with the SEC are: Ameren, 1-14756; Ameren Missouri, 1-2967; and Ameren Illinois, 1-3672.

Each registrant hereby undertakes to furnish to the SEC upon request a copy of any long-term debt instrument not listed above that such registrant has not filed as an exhibit pursuant to the exemption provided by Item 601(b)(4)(iii)(A) of Regulation S-K.

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SIGNATURES

Pursuant to the requirements of the Exchange Act, each registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized. The signature for each undersigned company shall be deemed to relate only to matters having reference to such company or its subsidiaries.

AMEREN CORPORATION
(Registrant)

/s/ Michael L. Moehn

Michael L. Moehn
Executive Vice President and Chief Financial Officer
(Principal Financial Officer)

UNION ELECTRIC COMPANY
(Registrant)

/s/ Michael L. Moehn

Michael L. Moehn
Executive Vice President and Chief Financial Officer
(Principal Financial Officer)

AMEREN ILLINOIS COMPANY
(Registrant)

/s/ Michael L. Moehn

Michael L. Moehn
Executive Vice President and Chief Financial Officer
(Principal Financial Officer)

Date: May 10, 2021

66

EX-31.1

Exhibit 31.1

RULE 13a-14(a)/15d-14(a) CERTIFICATION

OF PRINCIPAL EXECUTIVE OFFICER OF AMEREN CORPORATION

(required by Section 302 of the Sarbanes-Oxley Act of 2002)

    I, Warner L. Baxter, certify that:

    1.    I have reviewed this report on Form 10-Q for the quarterly period ended March 31, 2021 of Ameren Corporation;

    2.    Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

    3.    Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

    4.    The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a)Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b)Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c)Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

d)Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

    5.    The registrant’s other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a)All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

b)Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: May 10, 2021

 /s/ Warner L. Baxter

Warner L. Baxter
Chairman, President and Chief Executive Officer
(Principal Executive Officer)

EX-31.2

Exhibit 31.2

RULE 13a-14(a)/15d-14(a) CERTIFICATION

OF PRINCIPAL FINANCIAL OFFICER OF AMEREN CORPORATION

(required by Section 302 of the Sarbanes-Oxley Act of 2002)

    I, Michael L. Moehn, certify that:

    1.    I have reviewed this report on Form 10-Q for the quarterly period ended March 31, 2021 of Ameren Corporation;

    2.    Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

    3.    Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

    4.    The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a)Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b)Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c)Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

d)Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

    5.    The registrant’s other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a)All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

b)Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: May 10, 2021

 /s/ Michael L. Moehn

Michael L. Moehn
Executive Vice President and Chief Financial Officer
(Principal Financial Officer)

EX-31.3

Exhibit 31.3

RULE 13a-14(a)/15d-14(a) CERTIFICATION

OF PRINCIPAL EXECUTIVE OFFICER OF UNION ELECTRIC COMPANY

(required by Section 302 of the Sarbanes-Oxley Act of 2002)

    I, Martin J. Lyons, Jr., certify that:

    1.    I have reviewed this report on Form 10-Q for the quarterly period ended March 31, 2021 of Union Electric Company;

    2.    Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

    3.    Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

    4.    The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a)Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b)Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c)Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

d)Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

    5.    The registrant’s other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a)All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

b)Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: May 10, 2021

 /s/ Martin J. Lyons, Jr.

Martin J. Lyons, Jr.
Chairman and President
(Principal Executive Officer)

EX-31.4

Exhibit 31.4

RULE 13a-14(a)/15d-14(a) CERTIFICATION

OF PRINCIPAL FINANCIAL OFFICER OF UNION ELECTRIC COMPANY

(required by Section 302 of the Sarbanes-Oxley Act of 2002)

    I, Michael L. Moehn, certify that:

    1.    I have reviewed this report on Form 10-Q for the quarterly period ended March 31, 2021 of Union Electric Company;

    2.    Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

    3.    Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

    4.    The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a)Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b)Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c)Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

d)Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

    5.    The registrant’s other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a)All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

b)Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: May 10, 2021

 /s/ Michael L. Moehn

Michael L. Moehn
Executive Vice President and Chief Financial Officer
(Principal Financial Officer)

EX-31.5

Exhibit 31.5

RULE 13a-14(a)/15d-14(a) CERTIFICATION

OF PRINCIPAL EXECUTIVE OFFICER OF AMEREN ILLINOIS COMPANY

(required by Section 302 of the Sarbanes-Oxley Act of 2002)

    I, Richard J. Mark, certify that:

    1.    I have reviewed this report on Form 10-Q for the quarterly period ended March 31, 2021 of Ameren Illinois Company;

    2.    Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

    3.    Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

    4.    The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a)Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b)Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c)Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

d)Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

    5.    The registrant’s other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a)All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

b)Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: May 10, 2021

 /s/ Richard J. Mark

Richard J. Mark
Chairman and President
(Principal Executive Officer)

EX-31.6

Exhibit 31.6

RULE 13a-14(a)/15d-14(a) CERTIFICATION

OF PRINCIPAL FINANCIAL OFFICER OF AMEREN ILLINOIS COMPANY

(required by Section 302 of the Sarbanes-Oxley Act of 2002)

    I, Michael L. Moehn, certify that:

    1.    I have reviewed this report on Form 10-Q for the quarterly period ended March 31, 2021 of Ameren Illinois Company;

    2.    Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

    3.    Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

    4.    The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a)Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b)Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c)Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

d)Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

    5.    The registrant’s other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a)All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

b)Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: May 10, 2021

 /s/ Michael L. Moehn

Michael L. Moehn
Executive Vice President and Chief Financial Officer
(Principal Financial Officer)

EX-32.1

Exhibit 32.1

SECTION 1350 CERTIFICATION OF THE PRINCIPAL EXECUTIVE OFFICER

AND THE PRINCIPAL FINANCIAL OFFICER OF

AMEREN CORPORATION

(required by Section 906 of the Sarbanes-Oxley Act of 2002)

In connection with the report on Form 10-Q for the quarterly period ended March 31, 2021 of Ameren Corporation (the “Registrant”) as filed by the Registrant with the Securities and Exchange Commission on the date hereof (the "Form 10-Q”), each undersigned officer of the Registrant does hereby certify, pursuant to 18 U.S.C. §1350, as adopted pursuant to §906 of the Sarbanes-Oxley Act of 2002, that:

(1)The Form 10-Q fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 (15 U.S.C. 78m or 78o(d)); and

(2)The information contained in the Form 10-Q fairly presents, in all material respects, the financial condition and results of operations of the Registrant.

Date: May 10, 2021

 
 /s/ Warner L. Baxter

Warner L. Baxter
Chairman, President and Chief Executive Officer
(Principal Executive Officer)

 /s/ Michael L. Moehn

Michael L. Moehn
Executive Vice President and Chief Financial Officer
(Principal Financial Officer)

EX-32.2

Exhibit 32.2

SECTION 1350 CERTIFICATION OF THE PRINCIPAL EXECUTIVE OFFICER

AND THE PRINCIPAL FINANCIAL OFFICER OF

UNION ELECTRIC COMPANY

(required by Section 906 of the Sarbanes-Oxley Act of 2002)

In connection with the report on Form 10-Q for the quarterly period ended March 31, 2021 of Union Electric Company (the “Registrant”) as filed by the Registrant with the Securities and Exchange Commission on the date hereof (the "Form 10-Q"), each undersigned officer of the Registrant does hereby certify, pursuant to 18 U.S.C. §1350, as adopted pursuant to §906 of the Sarbanes-Oxley Act of 2002, that:

(1)The Form 10-Q fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 (15 U.S.C. 78m or 78o(d)); and

(2)The information contained in the Form 10-Q fairly presents, in all material respects, the financial condition and results of operations of the Registrant.

Date: May 10, 2021

 /s/ Martin J. Lyons, Jr.

Martin J. Lyons, Jr.
Chairman and President
(Principal Executive Officer)

 /s/ Michael L. Moehn

Michael L. Moehn
Executive Vice President and Chief Financial Officer
(Principal Financial Officer)

EX-32.3

Exhibit 32.3

SECTION 1350 CERTIFICATION OF THE PRINCIPAL EXECUTIVE OFFICER

AND THE PRINCIPAL FINANCIAL OFFICER OF

AMEREN ILLINOIS COMPANY

(required by Section 906 of the Sarbanes-Oxley Act of 2002)

In connection with the report on Form 10-Q for the quarterly period ended March 31, 2021 of Ameren Illinois Company (the “Registrant”) as filed by the Registrant with the Securities and Exchange Commission on the date hereof (the "Form 10-Q"), each undersigned officer of the Registrant does hereby certify, pursuant to 18 U.S.C. §1350, as adopted pursuant to §906 of the Sarbanes-Oxley Act of 2002, that:

(1)The Form 10-Q fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 (15 U.S.C. 78m or 78o(d)); and

(2)The information contained in the Form 10-Q fairly presents, in all material respects, the financial condition and results of operations of the Registrant.

Date: May 10, 2021

 /s/ Richard J. Mark

Richard J. Mark
Chairman and President
(Principal Executive Officer)

 /s/ Michael L. Moehn

Michael L. Moehn
Executive Vice President and Chief Financial Officer
(Principal Financial Officer)

XML

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	1-14756
Entity Registrant Name	Ameren Corporation
Entity Tax Identification Number	43-1723446
Entity Incorporation, State or Country Code	MO
Entity Address, Address Line One	1901 Chouteau Avenue
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63103
City Area Code	(314)
Local Phone Number	621-3222
Title of 12(b) Security	Common Stock, $0.01 par value per share
Trading Symbol(s)	AEE
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		255,552,619
Entity Central Index Key	0001002910
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false
Union Electric Company
Entity Information [Line Items]
Entity File Number	1-2967
Entity Registrant Name	Union Electric Company
Entity Tax Identification Number	43-0559760
Entity Incorporation, State or Country Code	MO
Entity Address, Address Line One	1901 Chouteau Avenue
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63103
City Area Code	(314)
Local Phone Number	621-3222
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		102,123,834
Entity Central Index Key	0000100826
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false
Ameren Illinois Company
Entity Information [Line Items]
Entity File Number	1-3672
Entity Registrant Name	Ameren Illinois Company
Entity Tax Identification Number	37-0211380
Entity Incorporation, State or Country Code	IL
Entity Address, Address Line One	10 Executive Drive
Entity Address, City or Town	Collinsville
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	62234
City Area Code	(618)
Local Phone Number	343-8150
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		25,452,373
Entity Central Index Key	0000018654
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false

XML

Consolidated Statement of Income (Loss) and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating Revenues:
Total operating revenues	$ 1,566	$ 1,440
Operating Expenses:
Fuel	65	140
Purchased power	191	134
Natural gas purchased for resale	165	107
Other operations and maintenance	420	438
Depreciation and amortization	281	255
Taxes other than income taxes	128	125
Total operating expenses	1,250	1,199
Operating Income	316	241
Other Income, Net	46	21
Interest Charges	100	93
Income Before Income Taxes	262	169
Income Taxes	27	21
Net Income	235	148
Less: Net Income Attributable to Noncontrolling Interests	2	2
Net Income Attributable to Ameren Common Shareholders	233	146
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	1	1
Comprehensive Income	236	149
Less: Comprehensive Income Attributable to Noncontrolling Interests	2	2
Comprehensive Income Attributable to Ameren Common Shareholders	$ 234	$ 147
Earnings Per Share, Basic and Diluted [Abstract]
Earnings per Common Share - Basic (in dollars per share)	$ 0.92	$ 0.59
Earnings per Common Share - Diluted (in dollars per share)	$ 0.91	$ 0.59
Weighted Average Common Shares Outstanding - Basic (in shares)	254.4	246.4
Weighted Average Number of Shares Outstanding - Diluted (in shares)	255.9	248.1
Electricity
Operating Revenues:
Total operating revenues	$ 1,156	$ 1,120
Natural Gas
Operating Revenues:
Total operating revenues	410	320
Union Electric Company
Operating Revenues:
Total operating revenues	704	680
Operating Expenses:
Fuel	65	140
Purchased power	88	39
Natural gas purchased for resale	31	18
Other operations and maintenance	225	239
Depreciation and amortization	156	139
Taxes other than income taxes	77	79
Total operating expenses	642	654
Operating Income	62	26
Other Income, Net	23	4
Interest Charges	39	40
Income Before Income Taxes	46	(10)
Income Taxes	(2)	(1)
Net Income	48	(9)
Preferred Stock Dividends	1	1
Net Income (Loss) Attributable to Parent	47	(10)
Union Electric Company | Electricity
Operating Revenues:
Total operating revenues	641	631
Union Electric Company | Natural Gas
Operating Revenues:
Total operating revenues	63	49
Ameren Illinois Company
Operating Revenues:
Total operating revenues	823	723
Operating Expenses:
Purchased power	106	98
Natural gas purchased for resale	134	89
Other operations and maintenance	194	199
Depreciation and amortization	115	107
Taxes other than income taxes	46	42
Total operating expenses	595	535
Operating Income	228	188
Other Income, Net	14	11
Interest Charges	42	39
Income Before Income Taxes	200	160
Income Taxes	50	39
Net Income	150	121
Preferred Stock Dividends	1	1
Net Income (Loss) Attributable to Parent	149	120
Ameren Illinois Company | Electricity
Operating Revenues:
Total operating revenues	476	452
Ameren Illinois Company | Natural Gas
Operating Revenues:
Total operating revenues	$ 347	$ 271

XML

Consolidated Statement of Income (Loss) and Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Pension and other postretirement benefit plan activity, tax	$ 0	$ 0

XML

Consolidated Balance Sheet - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Current Assets:
Cash and cash equivalents	$ 6	$ 139
Accounts receivable - trade (less allowance for doubtful accounts)	464	415
Unbilled revenue	210	269
Miscellaneous accounts receivable	61	65
Inventories	467	521
Restricted cash	134	17
Current regulatory assets	367	109
Other current assets	114	118
Total current assets	1,823	1,653
Property, Plant, and Equipment, Net	27,307	26,807
Investments and Other Assets:
Nuclear decommissioning trust fund	1,010	982
Goodwill	411	411
Regulatory assets	1,249	1,100
Other assets	989	1,077
Total investments and other assets	3,659	3,570
TOTAL ASSETS	32,789	32,030
Current Liabilities:
Current maturities of long-term debt	8	8
Short-term debt	889	490
Accounts and wages payable	581	958
Taxes accrued	128	82
Interest accrued	84	114
Current regulatory liabilities	225	121
Other current liabilities	392	407
Total current liabilities	2,307	2,180
Long-term Debt, Net	11,527	11,078
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	3,253	3,211
Regulatory liabilities	5,230	5,282
Asset retirement obligations	705	696
Pension and other postretirement benefits	38	37
Other deferred credits and liabilities	452	466
Total deferred credits and other liabilities	9,678	9,692
Commitments and Contingencies
Shareholders’ Equity:
Common Stock	3	3
Other paid-in capital, principally premium on common stock	6,295	6,179
Retained earnings	2,850	2,757
Accumulated other comprehensive loss	0	(1)
Total shareholders’ equity	9,148	8,938
Noncontrolling Interests	129	142
Total equity	9,277	9,080
TOTAL LIABILITIES AND EQUITY	32,789	32,030
Union Electric Company
Current Assets:
Cash and cash equivalents	1	136
Advances to money pool	0	139
Accounts receivable - trade (less allowance for doubtful accounts)	156	166
Accounts receivable – affiliates	69	57
Unbilled revenue	109	133
Miscellaneous accounts receivable	43	36
Inventories	362	386
Restricted cash	3	5
Current regulatory assets	141	60
Other current assets	70	79
Total current assets	951	1,192
Property, Plant, and Equipment, Net	14,221	13,879
Investments and Other Assets:
Nuclear decommissioning trust fund	1,010	982
Regulatory assets	413	347
Other assets	375	383
Total investments and other assets	1,798	1,712
TOTAL ASSETS	16,970	16,783
Current Liabilities:
Current maturities of long-term debt	8	8
Short-term debt	204	0
Accounts and wages payable	267	501
Accounts payable – affiliates	40	46
Taxes accrued	85	42
Interest accrued	46	53
Current asset retirement obligations	59	60
Other current liabilities	116	123
Total current liabilities	825	833
Long-term Debt, Net	5,096	5,096
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	1,756	1,742
Regulatory liabilities	3,130	3,110
Asset retirement obligations	700	691
Pension and other postretirement benefits	34	35
Other deferred credits and liabilities	59	66
Total deferred credits and other liabilities	5,679	5,644
Commitments and Contingencies
Shareholders’ Equity:
Common Stock	511	511
Other paid-in capital, principally premium on common stock	2,631	2,518
Preferred stock	80	80
Retained earnings	2,148	2,101
Total shareholders’ equity	5,370	5,210
TOTAL LIABILITIES AND EQUITY	16,970	16,783
Ameren Illinois Company
Current Assets:
Cash and cash equivalents	0	0
Accounts receivable - trade (less allowance for doubtful accounts)	293	234
Accounts receivable – affiliates	71	64
Unbilled revenue	101	136
Miscellaneous accounts receivable	5	12
Inventories	105	135
Restricted cash	125	6
Current regulatory assets	217	37
Other current assets	24	23
Total current assets	941	647
Property, Plant, and Equipment, Net	11,358	11,201
Investments and Other Assets:
Goodwill	411	411
Regulatory assets	820	742
Other assets	442	534
Total investments and other assets	1,673	1,687
TOTAL ASSETS	13,972	13,535
Current Liabilities:
Short-term debt	323	0
Borrowings from money pool	0	19
Accounts and wages payable	255	363
Accounts payable – affiliates	43	51
Customer deposits	70	74
Current regulatory liabilities	200	88
Other current liabilities	207	221
Total current liabilities	1,098	816
Long-term Debt, Net	3,947	3,946
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	1,430	1,367
Regulatory liabilities	1,988	2,063
Pension and other postretirement benefits	67	69
Environmental remediation	51	57
Other deferred credits and liabilities	249	251
Total deferred credits and other liabilities	3,785	3,807
Commitments and Contingencies
Shareholders’ Equity:
Common Stock	0	0
Other paid-in capital, principally premium on common stock	2,692	2,652
Preferred stock	49	62
Retained earnings	2,401	2,252
Total shareholders’ equity	5,142	4,966
TOTAL LIABILITIES AND EQUITY	$ 13,972	$ 13,535

XML

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Accounts Receivable, Allowance for Credit Loss, Current	$ 47	$ 50
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	400,000,000.0	400,000,000.0
Common Stock, Shares, Outstanding	255,500,000	253,300,000
Union Electric Company
Accounts Receivable, Allowance for Credit Loss, Current	$ 15	$ 16
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	150,000,000.0	150,000,000.0
Common Stock, Shares, Outstanding	102,100,000	102,100,000
Ameren Illinois Company
Accounts Receivable, Allowance for Credit Loss, Current	$ 32	$ 34
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	45,000,000.0	45,000,000.0
Common Stock, Shares, Outstanding	25,500,000	25,500,000

XML

Consolidated Statement of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash Flows From Operating Activities:
Net income	$ 235	$ 148
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	295	263
Amortization of nuclear fuel	0	23
Amortization of debt issuance costs and premium/discounts	5	5
Deferred income taxes and investment tax credits, net	26	23
Allowance for equity funds used during construction	(7)	(4)
Stock-based compensation costs	6	6
Other	8	17
Changes in assets and liabilities:
Receivables	(5)	(5)
Inventories	54	23
Accounts and wages payable	(252)	(221)
Taxes accrued	60	47
Regulatory assets and liabilities	(421)	(14)
Assets, other	(9)	(3)
Liabilities, other	(34)	(18)
Pension and other postretirement benefits	4	0
Net cash provided by (used in) operating activities	(35)	290
Cash Flows From Investing Activities:
Capital expenditures	(694)	(636)
Wind generation expenditures	(193)	0
Nuclear fuel expenditures	(1)	(35)
Purchases of securities – nuclear decommissioning trust fund	(152)	(96)
Sales and maturities of securities – nuclear decommissioning trust fund	150	81
Other	1	2
Net cash used in investing activities	(889)	(684)
Cash Flows From Financing Activities:
Dividends on common stock	(140)	(122)
Dividends paid to noncontrolling interest holders	(2)	(2)
Short-term debt, net	399	175
Maturities of long-term debt	0	(85)
Issuances of long-term debt	450	465
Issuances of common stock	125	13
Redemptions of Ameren Illinois preferred stock	(13)	0
Employee payroll taxes related to stock-based compensation	(17)	(20)
Debt issuance costs	(3)	(3)
Other	(4)	0
Net cash provided by financing activities	795	421
Net change in cash, cash equivalents, and restricted cash	(129)	27
Cash, cash equivalents, and restricted cash at beginning of year	301	176
Cash, cash equivalents, and restricted cash at end of period	172	203
Union Electric Company
Cash Flows From Operating Activities:
Net income	48	(9)
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	171	148
Amortization of nuclear fuel	0	23
Amortization of debt issuance costs and premium/discounts	1	2
Deferred income taxes and investment tax credits, net	4	(5)
Allowance for equity funds used during construction	(4)	(2)
Other	3	2
Changes in assets and liabilities:
Receivables	20	(3)
Inventories	24	(18)
Accounts and wages payable	(201)	(172)
Taxes accrued	39	55
Regulatory assets and liabilities	(164)	16
Assets, other	13	2
Liabilities, other	(9)	0
Pension and other postretirement benefits	4	2
Net cash provided by (used in) operating activities	(51)	41
Cash Flows From Investing Activities:
Capital expenditures	(341)	(278)
Wind generation expenditures	(193)	0
Nuclear fuel expenditures	(1)	(35)
Purchases of securities – nuclear decommissioning trust fund	(152)	(96)
Sales and maturities of securities – nuclear decommissioning trust fund	150	81
Money pool advances, net	139	0
Net cash used in investing activities	(398)	(328)
Cash Flows From Financing Activities:
Dividends on preferred stock	(1)	(1)
Short-term debt, net	204	(104)
Maturities of long-term debt	0	(85)
Issuances of long-term debt	0	465
Capital contributions from parent	113	0
Debt issuance costs	0	(3)
Net cash provided by financing activities	316	272
Net change in cash, cash equivalents, and restricted cash	(133)	(15)
Cash, cash equivalents, and restricted cash at beginning of year	145	39
Cash, cash equivalents, and restricted cash at end of period	12	24
Ameren Illinois Company
Cash Flows From Operating Activities:
Net income	150	121
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	115	106
Amortization of debt issuance costs and premium/discounts	3	2
Deferred income taxes and investment tax credits, net	53	22
Allowance for equity funds used during construction	(3)	(2)
Other	3	(2)
Changes in assets and liabilities:
Receivables	(24)	(6)
Inventories	30	41
Accounts and wages payable	(40)	(20)
Taxes accrued	3	16
Regulatory assets and liabilities	(255)	(28)
Assets, other	(15)	(4)
Liabilities, other	(9)	(14)
Pension and other postretirement benefits	(1)	(2)
Net cash provided by (used in) operating activities	13	232
Cash Flows From Investing Activities:
Capital expenditures	(337)	(324)
Other	0	1
Net cash used in investing activities	(337)	(323)
Cash Flows From Financing Activities:
Dividends on preferred stock	(1)	(1)
Short-term debt, net	323	7
Money pool borrowings, net	(19)	0
Capital contributions from parent	40	100
Redemption of preferred stock	(13)	0
Other	(4)	0
Net cash provided by financing activities	326	106
Net change in cash, cash equivalents, and restricted cash	2	15
Cash, cash equivalents, and restricted cash at beginning of year	147	125
Cash, cash equivalents, and restricted cash at end of period	$ 149	$ 140

XML

Consolidated Statement of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Other Paid-in Capital	Retained Earnings	Deferred Retirement Benefit Costs	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	Total Ameren Corporation Shareholders' Equity	Union Electric Company	Union Electric Company Common Stock	Union Electric Company Other Paid-in Capital	Union Electric Company Preferred Stock	Union Electric Company Retained Earnings	Ameren Illinois Company	Ameren Illinois Company Common Stock	Ameren Illinois Company Other Paid-in Capital	Ameren Illinois Company Preferred Stock	Ameren Illinois Company Retained Earnings
Beginning of year at Dec. 31, 2019			$ 5,694	$ 2,380	$ (17)		$ 142				$ 2,027		$ 1,731			$ 2,188	$ 62	$ 1,882
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Settlement of forward sale agreement through common shares issuance			0
Shares issued under the DRPlus and 401(k) plan			13
Stock-based compensation activity			(12)
Capital contribution from parent									$ 0		0			$ (100)		100
Net income	$ 148								(9)				(9)	121				121
Net income attributable to Ameren common shareholders	146			146
Dividends on common stock				(122)
Preferred stock dividends													(1)					(1)
Change in deferred retirement benefit costs	1				1
Net income attributable to noncontrolling interest holders	$ (2)						2
Dividends paid to noncontrolling interest holders							(2)
Redemptions of preferred stock			0													0
Common stock shares outstanding at beginning of year (in shares) at Dec. 31, 2019	246,200,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan (in shares)	200,000
Shares issued for stock-based compensation (in shares)	500,000
Common stock shares outstanding at end of period (in shares) at Mar. 31, 2020	246,900,000
End of period at Mar. 31, 2020	$ 8,227	$ 2	5,695	2,404	(16)	$ (16)	142			$ 511	2,027	$ 80	1,721		$ 0	2,288	62	2,002
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share (in dollars per share)	$ 0.495
Shareholders' equity, end of year at Mar. 31, 2020								$ 8,085	4,339					4,352
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under forward sale agreement (in shares)	0
Beginning of year at Dec. 31, 2020	$ 9,080		6,179	2,757	(1)		142				2,518		2,101			2,652	62	2,252
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Settlement of forward sale agreement through common shares issuance			113
Shares issued under the DRPlus and 401(k) plan			12
Stock-based compensation activity			(9)
Capital contribution from parent									(113)		113			(40)		40
Net income	235								$ 48				48	$ 150				150
Net income attributable to Ameren common shareholders	233			233
Dividends on common stock				(140)
Preferred stock dividends													(1)					(1)
Change in deferred retirement benefit costs	1				1
Net income attributable to noncontrolling interest holders	$ (2)						2
Dividends paid to noncontrolling interest holders							(2)
Redemptions of preferred stock			13													13
Common stock shares outstanding at beginning of year (in shares) at Dec. 31, 2020	253,300,000								102,100,000					25,500,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan (in shares)	100,000
Shares issued for stock-based compensation (in shares)	500,000
Common stock shares outstanding at end of period (in shares) at Mar. 31, 2021	255,500,000								102,100,000					25,500,000
End of period at Mar. 31, 2021	$ 9,277	$ 3	$ 6,295	$ 2,850	$ 0	$ 0	$ 129			$ 511	$ 2,631	$ 80	$ 2,148		$ 0	$ 2,692	$ 49	$ 2,401
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share (in dollars per share)	$ 0.550
Shareholders' equity, end of year at Mar. 31, 2021	$ 9,148							$ 9,148	$ 5,370					$ 5,142
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under forward sale agreement (in shares)	1,600,000

XML

Summary Of Significant Accounting Policies

3 Months Ended

Mar. 31, 2021

Accounting Policies [Abstract]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

General

Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren has other subsidiaries that conduct other activities, such as providing shared services.

•Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri.

•Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois.

•ATXI operates a FERC rate-regulated electric transmission business in the MISO.

The COVID-19 pandemic continues to affect our results of operations, financial position, and liquidity, but we expect a gradual improvement in sales volumes in 2021, compared to 2020. In the first three months of 2021, our sales volumes were comparable to the same period in 2020, excluding the estimated effects of weather and customer energy-efficiency programs. However, we experienced an increase in our accounts receivable balances that were past due or that were a part of a deferred payment arrangement, and a decline in our cash collections from customers. The continued effect of the COVID-19 pandemic on our results of operations, financial position, and liquidity in subsequent periods will depend on its severity and longevity, future regulatory or legislative actions with respect thereto, and the resulting impact on business, economic, and capital market conditions. In general, restrictions on social activities and nonessential businesses implemented in our service territories in 2020 have been relaxed. However, certain restrictions remain in place that limit individual activities and the operation of nonessential businesses and additional restrictions may be imposed in the future.

We continue to assess the impacts the COVID-19 pandemic is having on our businesses, including but not limited to impacts on our liquidity; demand for residential, commercial, and industrial electric and natural gas services; changes in deferred payment arrangements for customers; the timing and extent to which recovery of incremental costs incurred, net of savings, and forgone customer late fee revenues at Ameren Missouri is allowed by the MoPSC; changes in our ability to disconnect customers for nonpayment; bad debt expense; supply chain operations; the availability of our employees and contractors; counterparty credit; capital construction; infrastructure operations and maintenance; energy-efficiency programs; and pension valuations. In March 2021, the MoPSC approved accounting authority orders that allowed Ameren Missouri to accumulate $9 million of certain costs incurred related to the COVID-19 pandemic, net of savings, as well as forgone customer late fees and reconnection fee revenues from March 2020 to March 2021, for potential recovery in the current electric and natural gas service regulatory rate reviews. While the revenues from Ameren Illinois’ electric distribution business, residential and small nonresidential customers of Ameren Illinois’ natural gas distribution business, and Ameren Illinois’ and ATXI’s electric transmission businesses are decoupled from changes in sales volumes, earnings at Ameren Missouri and those associated with Ameren Illinois’ large nonresidential natural gas customers are exposed to such changes. Regarding uncollectible accounts receivable, Ameren Illinois’ electric distribution and natural gas distribution businesses have bad debt riders, which provide for recovery of bad debt write-offs, net of any subsequent recoveries. Ameren Missouri does not have a bad debt rider or tracker, and thus its earnings are exposed to increases in bad debt expense, absent regulatory relief. However, Ameren Missouri does not expect a material impact to earnings from increases in bad debt expense. As of March 31, 2021, accounts receivable balances that were 30 days or greater past due or that were a part of a deferred payment arrangement represented 27%, 19%, and 32%, or $137 million, $33 million, and $104 million, of Ameren’s, Ameren Missouri’s, and Ameren Illinois’ customer trade receivables before allowance for doubtful accounts, respectively. As of March 31, 2020, these percentages were 21%, 16%, and 25%, or $99 million, $29 million, and $70 million, for Ameren, Ameren Missouri, and Ameren Illinois, respectively. For information regarding Ameren Illinois’ suspension and subsequent reinstatement of customer disconnections and late fee charges for nonpayment and Ameren Missouri’s accounting authority orders related to the COVID-19 pandemic, see Note 2 – Rate and Regulatory Matters below.

Ameren’s financial statements are prepared on a consolidated basis and therefore include the accounts of its majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Missouri and Ameren Illinois have no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated.

Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair statement of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates. The results of operations of an interim period may not give a true indication of results that may be expected for a full year. These financial statements should be read in conjunction with the financial statements and accompanying notes included in the Form 10-K.

Variable Interest Entities

As of March 31, 2021, and December 31, 2020, Ameren had unconsolidated variable interests as a limited partner in various equity method investments, totaling $41 million and $37 million, respectively, included in “Other assets” on Ameren’s consolidated balance sheet. Ameren is not the primary beneficiary of these investments because it does not have the power to direct matters that most significantly affect the activities of these variable interest entities. As of March 31, 2021, the maximum exposure to loss related to these variable interests is limited to the investment in these partnerships of $41 million plus associated outstanding funding commitments of $33 million.

Company-owned Life Insurance

Ameren and Ameren Illinois have company-owned life insurance, which is recorded at the net cash surrender value. The net cash surrender value is the amount that can be realized under the insurance policies at the balance sheet date. As of March 31, 2021, the cash surrender value of company-owned life insurance at Ameren and Ameren Illinois was $275 million (December 31, 2020 – $272 million) and $117 million (December 31, 2020 – $115 million), respectively, while total borrowings against the policies were $107 million (December 31, 2020 – $107 million) at both Ameren and Ameren Illinois. Ameren and Ameren Illinois have the right to offset the borrowings against the cash surrender value of the policies and, consequently, present the net asset in “Other assets” on their respective balance sheets.

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Rate And Regulatory Matters

3 Months Ended

Mar. 31, 2021

Public Utilities, General Disclosures [Abstract]

RATE AND REGULATORY MATTERS

RATE AND REGULATORY MATTERS

Below is a summary of updates to significant regulatory proceedings and related legal proceedings. See Note 2 – Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K for additional information and a summary of our regulatory frameworks. We are unable to predict the ultimate outcome of these matters, the timing of final decisions of the various agencies and courts, or the impact on our results of operations, financial position, or liquidity.

Missouri

2021 Electric Service Regulatory Rate Review

In March 2021, Ameren Missouri filed a request with the MoPSC seeking approval to increase its annual revenues for electric service by $299 million. The electric rate increase request is based on a 9.9% ROE, a capital structure composed of 51.9% common equity, a rate base of $10.0 billion, and a test year ended December 31, 2020, with certain pro-forma adjustments expected through an anticipated true-up date of September 30, 2021. Ameren Missouri also requested the continued use of the FAC and trackers for pension and postretirement benefits, uncertain income tax positions, and certain excess deferred income taxes that the MoPSC previously authorized in earlier electric rate orders. Additionally, Ameren Missouri requested to recover certain estimated costs associated with the Meramec Energy Center, which is expected to be retired in 2022, over a five-year period. Ameren Missouri requested the use of a tracker for any variances between certain costs collected in customer rates associated with the Meramec Energy Center and actual costs incurred after the date new rates become effective, which would be considered for recovery or refund in a future electric regulatory rate review. The electric rate increase request reflects the following:

•increased infrastructure investments made under Ameren Missouri’s Smart Energy Plan;

•the impact of the transition to a cleaner generation portfolio, including advancing the retirement dates of the Sioux and Rush Island energy centers consistent with Ameren Missouri’s 2020 IRP and 700 MWs of wind generation investment for the High Prairie and Atchison renewable energy centers, which are mitigated by reductions resulting from the request to recover certain Meramec Energy Center costs over a five-year period and the associated tracker;

•decreased weather-normalized customer sales volumes; and

•increased pension and other post-retirement benefits and tax amortization expenses, partially offset by decreased other operations and maintenance expenses.

The MoPSC proceeding relating to the proposed electric service rate changes will take place over a period of up to 11 months, with a decision by the MoPSC expected by February 2022 and new rates effective by March 2022. Ameren Missouri cannot predict the level of any electric service rate change the MoPSC may approve, whether the requested regulatory recovery mechanisms will be approved, or whether

any rate change that may eventually be approved will be sufficient for Ameren Missouri to recover its costs and earn a reasonable return on its investments when the rate change goes into effect.

Wind Generation Facility

In January 2021, Ameren Missouri acquired an up-to 300-MW wind generation project located in northwestern Missouri and partially placed it in service as the Atchison Renewable Energy Center. As of the date of this filing, Ameren Missouri has placed approximately half of the project in service, representing a purchase price of approximately $250 million, including an immaterial amount of transaction costs. Ameren Missouri expects the remaining MWs of the project to be in service by the end of September 2021. The Atchison Renewable Energy Center will support Ameren Missouri’s compliance with the Missouri renewable energy standard.

2021 Natural Gas Delivery Service Regulatory Rate Review

In March 2021, Ameren Missouri filed a request with the MoPSC seeking approval to increase its annual revenues for natural gas delivery service by $9 million. The natural gas rate increase request is based on a 9.8% ROE, a capital structure composed of 51.9% common equity, a rate base of $310 million, and a test year ended December 31, 2020, with certain pro-forma adjustments expected through an anticipated true-up date of September 30, 2021. The request includes the continued use of the PGA, ISRS, and DCA and trackers for pension and other postretirement benefits and certain excess deferred taxes that the MoPSC previously authorized in earlier natural gas rate orders.

The MoPSC proceeding relating to the proposed natural gas delivery service rate changes will take place over a period of up to 11 months, with a decision by the MoPSC expected by February 2022 and new rates effective by March 2022. Ameren Missouri cannot predict the level of any natural gas delivery service rate change the MoPSC may approve, or whether any rate change that may eventually be approved will be sufficient for Ameren Missouri to recover its costs and earn a reasonable return on its investments when the rate change goes into effect.

Accounting Authority Orders Related to COVID-19 Pandemic Costs

In March 2021, the MoPSC issued orders approving nonunanimous stipulation and agreements related to Ameren Missouri’s electric and natural gas service accounting authority order requests. The orders allowed Ameren Missouri to accumulate $9 million of certain costs incurred related to the COVID-19 pandemic, net of cost savings, as well as forgone customer late fee and reconnection fee revenues from March 2020 to March 2021, for potential recovery in the electric and natural gas service regulatory rate reviews discussed above. As of March 31, 2021, Ameren Missouri deferred other operations and maintenance expenses of $5 million as a regulatory asset related to the accounting authority orders. If approved for recovery, Ameren Missouri would recognize the remaining $4 million associated with forgone customer late fee and reconnection fee revenue when billed to customers.

Illinois

Electric Distribution Service Rates

In April 2021, Ameren Illinois filed its annual electric distribution service performance-based formula rate update with the ICC, requesting an increase of $64 million in its rates. This update reflects an increase to the annual performance-based formula rate based on 2020 actual costs, an increase to include the 2020 revenue requirement reconciliation adjustment, and an increase for the conclusion of the 2019 revenue requirement reconciliation adjustment, which will be fully refunded to customers in 2021, consistent with the ICC’s December 2020 annual update filing order. It also reflects an increase based on expected net plant additions for 2021. An ICC decision in this proceeding is expected by December 2021, with new rates effective January 2022.

Electric Distribution Service Rate Reconciliation Tariff

In March 2021, the ICC issued an order approving Ameren Illinois’ requested tariff to reconcile its electric distribution service revenue requirement for a period of up to two years after the final customer rate update under performance-based formula ratemaking. To utilize the reconciliation, the ICC-approved tariff requires Ameren Illinois to file a traditional regulatory rate review for its electric distribution service, which may be based on a future test year, by the end of March in the year following the last year in which an annual performance-based formula rate update was permitted. Pursuant to this order, and without legislative change or Ameren Illinois’ election to no longer use performance-based formula ratemaking, Ameren Illinois’ 2022 and 2023 revenues would reflect each year’s actual costs, year-end rate base, and a return at the applicable WACC, with the ROE based on the annual average of the monthly yields of the 30-year United States Treasury bonds plus 580 basis points. The revenue requirement adjustment will be collected from, or refunded to, customers within two years from the end of the reconciled year.

Electric Energy Efficiency Plan

In March 2021, Ameren Illinois filed with the ICC an energy-efficiency plan which includes annual investments in electric energy-efficiency programs up to approximately $100 million per year from 2022 through 2025. The ICC has the ability to reduce the amount of electric energy-efficiency savings goals in future plan program years if there are insufficient cost-effective programs available, which could reduce the investments in electric energy-efficiency programs. The electric energy-efficiency program investments and the return on those investments are collected from customers through a rider and are not included in the electric distribution service performance-based formula ratemaking framework. A decision by the ICC in this proceeding is expected by September 2021.

QIP Reconciliation Order

In March 2021, the ICC issued an order approving Ameren Illinois’ QIP reconciliation for 2018. The ICC also found that Ameren Illinois’ natural gas capital investments recovered under the QIP during 2018 were accurate and prudent. The ICC order effectively dismissed the Illinois Attorney General’s challenge with respect to 2018 capital investments.

Service Disconnection Moratorium

From March 2020 through March 2021, the ICC limited disconnection activities and late fees for customer nonpayment to varying degrees based on customer class. In March 2021, the ICC issued an order allowing Ameren Illinois to resume disconnection activities for all residential customers through a phased-in approach, which began in April 2021 for customers with the largest past due balances and will resume by June 2021 for all remaining residential customers. The March 2021 order also requires Ameren Illinois to offer deferred payment arrangements, extending to 18 months, to all residential customers through June 2021. In addition, the order requires Ameren Illinois to extend the financial assistance program established by a June 2020 ICC order through 2021. Ameren Illinois is allowed to recover up to $4 million in costs incurred during 2021 related to this financial assistance program. These costs will be deferred as regulatory assets and the portion associated with Ameren Illinois’ electric distribution business will be recovered through its bad debt rider and the portion associated with its natural gas distribution business will be recovered through a special purpose rider.

Federal

Transmission Formula Rate Revisions

In February 2020, the MISO, on behalf of Ameren Missouri, Ameren Illinois, and ATXI, filed requests with the FERC to revise each company’s transmission formula rate calculations with respect to the calculation used for materials and supplies inventories included in rate base. In May 2020, the FERC issued orders approving the revisions prospectively. In addition, the FERC declined to order refunds for earlier periods, as requested by intervenors in Ameren Illinois’ filing, but directed its audit staff to review historical rate recovery in connection with an ongoing FERC audit. In June 2020, Ameren Missouri, Ameren Illinois, and ATXI filed requests for rehearing arguing, among other things, the revisions should be applied retrospectively to include the period January 1, 2019, to June 1, 2020, and that the FERC should not require refunds for periods prior to 2019. In July 2020, the FERC denied the rehearing requests without addressing the issues raised. In July 2020, Ameren Missouri, Ameren Illinois, and ATXI filed an appeal of the July 2020 rehearing denials to the United States Court of Appeals for the District of Columbia Circuit, which is under no deadline to address the appeal. In October 2020, the FERC issued an order reaffirming its May 2020 order and denying the arguments raised in the rehearing requests filed by Ameren Missouri, Ameren Illinois, and ATXI. Regardless of the outcome of the appeal, the impacts of the May 2020 and October 2020 orders are not expected to be material to Ameren’s, Ameren Missouri’s, or Ameren Illinois’ results of operations, financial position, or liquidity.

In March 2021, the FERC issued an order related to an intervenor challenge to Ameren Illinois’ 2020 transmission formula rate update. As a result of this order, in March 2021, Ameren Illinois recorded a regulatory liability of $9 million, largely as a reduction of electric operating revenues, to reflect expected refunds, including interest, primarily related to the historical rate recovery of materials and supplies inventories included in rate base. In April 2021, Ameren Illinois filed a request for rehearing with the FERC regarding its March 2021 order.

FERC Complaint Cases

In November 2013, a customer group filed a complaint case with the FERC seeking a reduction in the allowed base ROE for FERC-regulated transmission rate base under the MISO tariff from 12.38% to 9.15%. In September 2016, the FERC issued an order in the November 2013 complaint case, which lowered the allowed base ROE to 10.32%, or a 10.82% total allowed ROE with the inclusion of a 50 basis point incentive adder for participation in an RTO, that was effective from late September 2016 forward. The September 2016 order also required refunds for the period November 2013 to February 2015, which were paid in 2017. In November 2019, the FERC issued an order addressing the November 2013 complaint case, which set the allowed base ROE at 9.88%, superseding the 10.32% previously ordered, and required refunds, with interest, for the periods November 2013 to February 2015 and from late September 2016 forward. In December 2019, the MISO transmission owners, including Ameren Missouri, Ameren Illinois, and ATXI, filed requests for rehearing with the FERC. In May 2020, the FERC issued an order addressing the requests for rehearing, which set the allowed base ROE at 10.02%, superseding the 9.88%

previously ordered, and required refunds, with interest, for the periods November 2013 to February 2015 and from late September 2016 forward. In June 2020, various parties filed requests for rehearing with the FERC, challenging the new ROE methodology established by the May 2020 order. In July 2020, the FERC denied the rehearing requests without addressing the issues raised, and indicated it will address the requests for rehearing in a future order. Also in July 2020, Ameren Missouri, Ameren Illinois, and ATXI filed an appeal of the May 2020 order to the United States Court of Appeals for the District of Columbia Circuit challenging the refunds required for the period from September 2016 to May 2020. The court is under no deadline to address the appeal.

As of March 31, 2021, Ameren and Ameren Illinois had recorded current regulatory liabilities of $17 million and $9 million, respectively, to reflect the expected refunds, including interest, associated with the allowed base ROE set by the May 2020 order in the November 2013 complaint case. The increase in the FERC-allowed base ROE resulting from the May 2020 order is not material to Ameren Missouri’s results of operations, financial position, or liquidity.

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Short-Term Debt And Liquidity

3 Months Ended

Mar. 31, 2021

Debt Disclosure [Abstract]

SHORT-TERM DEBT AND LIQUIDITY

SHORT-TERM DEBT AND LIQUIDITY

The liquidity needs of the Ameren Companies are typically supported through the use of available cash, drawings under committed credit agreements, commercial paper issuances, and, in the case of Ameren Missouri and Ameren Illinois, short-term affiliate borrowings. See Note 4 – Short-term Debt and Liquidity under Part II, Item 8, in the Form 10-K for a description of our indebtedness provisions and other covenants as well as a description of money pool arrangements.

Short-Term Borrowings

The Missouri Credit Agreement and the Illinois Credit Agreement are available to support issuances under Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper programs, respectively, subject to borrowing sublimits, and the issuance of letters of credit. As of March 31, 2021, based on commercial paper outstanding and letters of credit issued under the Credit Agreements, along with cash and cash equivalents, the net liquidity available to Ameren (parent), Ameren Missouri, and Ameren Illinois, collectively, was $1.4 billion. The Ameren Companies were in compliance with the covenants in their Credit Agreements as of March 31, 2021. As of March 31, 2021, the ratios of consolidated indebtedness to consolidated total capitalization, calculated in accordance with the provisions of the Credit Agreements, were 57%, 49%, and 46% for Ameren, Ameren Missouri, and Ameren Illinois, respectively.

The following table presents commercial paper outstanding, net of issuance discounts, as of March 31, 2021, and December 31, 2020. There were no borrowings outstanding under the Credit Agreements as of March 31, 2021, or December 31, 2020.

	March 31, 2021		December 31, 2020
Ameren (parent)	$	362	$	490
Ameren Missouri	204		—
Ameren Illinois	323		—
Ameren consolidated	$	889	$	490

The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances and borrowings under the Credit Agreements in the aggregate for the three months ended March 31, 2021 and 2020:

	Ameren (parent)			Ameren Missouri				Ameren Illinois			Ameren Consolidated
2021
Average daily amount outstanding	$	454		$	99			$	96		$	649
Weighted-average interest rate	0.25		%	0.22		%		0.21		%	0.24		%
Peak amount outstanding during period(a)	$	650		$	206			$	353		$	916
Peak interest rate	0.33		%	0.25		%		0.25		%	0.33		%
2020
Average daily amount outstanding	$	157		$	395			$	76		$	628
Weighted-average interest rate	1.94		%	1.86		%		1.99		%	1.89		%
Peak amount outstanding during period(a)	$	425		$	573			$	150		$	908
Peak interest rate	3.30		%	5.05		%	(b)	3.40		%	5.05		%	(b)

(a)The timing of peak outstanding commercial paper issuances and borrowings under the Credit Agreements varies by company. Therefore, the sum of individual company peak amounts may not equal the Ameren consolidated peak for the period.

(b)Ameren’s and Ameren Missouri’s peak interest rate was affected by temporary disruptions in the commercial paper market in the first quarter of 2020.

Money Pools

Ameren has money pool agreements with and among its subsidiaries to coordinate and provide for certain short-term cash and working capital requirements. The average interest rate for borrowings under the utility money pool for the three months ended March 31, 2021, was 0.22% (2020 – 1.93%). See Note 8 – Related-party Transactions for the amount of interest income and expense from the utility money pool arrangements recorded by Ameren Missouri and Ameren Illinois for the three months ended March 31, 2021 and 2020.

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Long-Term Debt And Equity Financings

3 Months Ended

Mar. 31, 2021

Long-Term Debt And Equity Financings [Abstract]

LONG-TERM DEBT AND EQUITY FINANCINGS

LONG-TERM DEBT AND EQUITY FINANCINGS

Ameren

For the three months ended March 31, 2021, Ameren issued a total of 0.1 million shares of common stock under its DRPlus and 401(k) plan, and received proceeds of $12 million. In addition, in the first quarter of 2021, Ameren issued 0.5 million shares of common stock valued at $33 million upon the vesting of stock-based compensation.

In February 2021, Ameren settled the remainder of the forward sale agreement by physically delivering 1.6 million shares of common stock for cash proceeds of $113 million. The proceeds were used to fund a portion of Ameren Missouri’s wind generation investments. See Note 2 - Rate and Regulatory Matters for additional information about the wind generation investments.

In March 2021, Ameren (parent) issued $450 million of 1.75% senior unsecured notes due March 2028, with interest payable semiannually on March 15 and September 15 of each year, beginning September 15, 2021. Ameren received net proceeds of $447 million, which were used for general corporate purposes, including the repayment of short-term debt.

Ameren Missouri

Ameren Missouri received capital contributions totaling $113 million from Ameren (parent) during the three months ended March 31, 2021.

Ameren Illinois

In March 2021, Ameren Illinois redeemed its 6.625% and 7.75% series preferred stock at par for $12 million and $1 million, respectively. The preferred stock of Ameren Illinois is reflected in “Noncontrolling Interests” on Ameren’s consolidated balance sheet.

Ameren Illinois received capital contributions totaling $40 million from Ameren (parent) during the three months ended March 31, 2021.

Indenture Provisions and Other Covenants

See Note 5 – Long-Term Debt and Equity Financings under Part II, Item 8, in the Form 10-K for a description of our indenture provisions and other covenants, as well as restrictions on the payment of dividends. At March 31, 2021, the Ameren Companies were in compliance with the provisions and covenants contained in their indentures and articles of incorporation, as applicable, and ATXI was in compliance with the provisions and covenants contained in its note purchase agreement.

Off-balance-sheet Arrangements

At March 31, 2021, none of the Ameren Companies had any significant off-balance-sheet financing arrangements, other than variable interest entities. See Note 1 – Summary of Significant Accounting Policies for further detail concerning variable interest entities.

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Other Income and Expenses

3 Months Ended

Mar. 31, 2021

Other Nonoperating Income (Expense) [Abstract]

OTHER INCOME AND EXPENSES

OTHER INCOME, NET

The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the three months ended March 31, 2021 and 2020:

	Three Months
	2021		2020
Ameren:
Allowance for equity funds used during construction	$	7	$	4
Interest income on industrial development revenue bonds	6		6
Other interest income	1		1
Non-service cost components of net periodic benefit income(a)	34		23
Miscellaneous income	4		2
Donations	(3)		(13)		(b)
Miscellaneous expense	(3)		(2)
Total Other Income, Net	$	46	$	21
Ameren Missouri:
Allowance for equity funds used during construction	$	4	$	2
Interest income on industrial development revenue bonds	6		6
Non-service cost components of net periodic benefit income(a)	14		5
Miscellaneous income	1		1
Donations	—		(8)		(b)
Miscellaneous expense	(2)		(2)
Total Other Income, Net	$	23	$	4
Ameren Illinois:
Allowance for equity funds used during construction	$	3	$	2
Interest income	1		1
Non-service cost components of net periodic benefit income	14		13
Miscellaneous income	—		1
Donations	(3)		(4)
Miscellaneous expense	(1)		(2)
Total Other Income, Net	$	14	$	11

(a)For the three months ended March 31, 2021 and 2020, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of less than $(1) million and $6 million, respectively, due to a regulatory tracking mechanism for the difference between the level of such costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates.

(b)Includes $8 million pursuant to Ameren Missouri’s March 2020 electric rate order. See Note 2 – Rate and Regulatory Matters under Part II, Item 8, in the Form 10-K for additional information.

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Derivative Financial Instruments

3 Months Ended

Mar. 31, 2021

Derivative Instruments and Hedging Activities Disclosure [Abstract]

DERIVATIVE FINANCIAL INSTRUMENTS

DERIVATIVE FINANCIAL INSTRUMENTS

We use derivatives to manage the risk of changes in market prices for natural gas and power, as well as the risk of changes in rail transportation surcharges through fuel oil hedges. Such price fluctuations may cause the following:

•an unrealized appreciation or depreciation of our contracted commitments to purchase or sell when purchase or sale prices under the commitments are compared with current commodity prices;

•market values of natural gas inventories that differ from the cost of those commodities in inventory;

•actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays; and

•actual off-system sales revenues that differ from anticipated revenues

The derivatives that we use to hedge these risks are governed by our risk management policies for forward contracts, futures, options, and swaps. Our net positions are continually assessed within our structured hedging programs to determine whether new or offsetting transactions are required. The goal of the hedging program is generally to mitigate financial risks while ensuring that sufficient volumes are available to meet our requirements. Contracts we enter into as part of our risk management program may be settled financially, settled by physical delivery, or net settled with the counterparty.

All contracts considered to be derivative instruments are required to be recorded on the balance sheet at their fair values, unless the NPNS exception applies. Many of our physical contracts, such as our purchased power contracts, qualify for the NPNS exception to derivative accounting rules. The revenue or expense on NPNS contracts is recognized at the contract price upon physical delivery. The following disclosures exclude NPNS contracts and other non-derivative commodity contracts that are accounted for under the accrual method of accounting.

If we determine that a contract meets the definition of a derivative and is not eligible for the NPNS exception, we review the contract to determine whether the resulting gains or losses qualify for regulatory deferral. Derivative contracts that qualify for regulatory deferral are recorded at fair value, with changes in fair value recorded as regulatory assets or liabilities in the period in which the change occurs. We believe derivative losses and gains deferred as regulatory assets and liabilities are probable of recovery, or refund, through future rates charged to customers. Regulatory assets and liabilities are amortized to operating income as related losses and gains are reflected in rates charged to customers. Therefore, gains and losses on these derivatives have no effect on operating income. As of March 31, 2021, and December 31, 2020, all contracts that met the definition of a derivative and were not eligible for the NPNS exception received regulatory deferral. Cash flows for all derivative financial instruments are classified in cash flows from operating activities.

The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of March 31, 2021, and December 31, 2020. As of March 31, 2021, these contracts extended through October 2023, October 2026, and May 2032 for fuel oils, natural gas and power, respectively.

	Quantity (in millions, except as indicated)
	March 31, 2021			December 31, 2020
Commodity	Ameren Missouri	Ameren Illinois	Ameren	Ameren Missouri	Ameren Illinois	Ameren
Fuel oils (in gallons)	36	—	36	43	—	43
Natural gas (in mmbtu)	34	114	148	33	114	147
Power (in MWhs)	7	7	14	6	7	13

The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments, as of March 31, 2021, and December 31, 2020:

			March 31, 2021					December 31, 2020
	Balance Sheet Location		Ameren Missouri		Ameren Illinois		Ameren			Ameren Missouri		Ameren Illinois		Ameren
Fuel oils	Other current assets	$	2	$	—	$	2		$	2	$	—	$	2
	Other assets		3		—		3			—		—		—
Natural gas	Other current assets		2		10		12			1		8		9
	Other assets		2		4		6			2		2		4
Power	Other current assets		4		—		4			7		—		7
	Other assets		1		—		1			—		—		—
	Total assets	$	14	$	14	$	28		$	12	$	10	$	22
Fuel oils	Other current liabilities	$	3	$	—	$	3		$	7	$	—	$	7
	Other deferred credits and liabilities		—		—		—			2		—		2
Natural gas	Other current liabilities		—		—		—			1		1		2
	Other deferred credits and liabilities		—		—		—			—		1		1
Power	Other current liabilities		9		16		25			3		17		20
	Other deferred credits and liabilities		5		169		174			8		181		189
	Total liabilities	$	17	$	185	$	202		$	21	$	200	$	221

The Ameren Companies elect to present the fair value amounts of derivative assets and derivative liabilities subject to an enforceable master netting arrangement or similar agreement at the gross amounts on the balance sheet. However, if the gross amounts recognized on the balance sheet were netted with derivative instruments and cash collateral received or posted, the net amounts would not be materially different from the gross amounts at March 31, 2021, and December 31, 2020.

Credit Risk

In determining our concentrations of credit risk related to derivative instruments, we review our individual counterparties and categorize each counterparty into groupings according to the primary business in which each engages. As of March 31, 2021, if counterparty groups were to fail completely to perform on contracts, the Ameren Companies’ maximum exposure related to derivative assets would have been immaterial with or without consideration of the application of master netting arrangements or similar agreements and collateral held.

Certain of our derivative instruments contain collateral provisions tied to the Ameren Companies’ credit ratings. If our credit ratings were downgraded below investment grade, or if a counterparty with reasonable grounds for uncertainty regarding our ability to satisfy an obligation requested adequate assurance of performance, additional collateral postings might be required. The additional collateral required is the net liability position allowed under master netting arrangements or similar agreements, assuming (1) the credit risk-related contingent features underlying these arrangements were triggered and (2) those counterparties with rights to do so requested collateral. As of March 31, 2021, the aggregate fair value of derivative instruments with credit risk-related contingent features in a gross liability position, the cash collateral posted, and the aggregate amount of additional collateral that counterparties could require were each immaterial to Ameren, Ameren

Missouri, and Ameren Illinois.

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Fair Value Measurements

3 Months Ended

Mar. 31, 2021

Fair Value Disclosures [Abstract]

Fair Value Disclosures

FAIR VALUE MEASUREMENTS

Fair value is defined as the price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Fair value measurements are classified in three levels based on the fair value hierarchy as defined by GAAP. See Note 8 – Fair Value Measurements under Part II, Item 8, of the Form 10-K for information related to hierarchy levels and valuation techniques.

We consider nonperformance risk in our valuation of derivative instruments by analyzing our own credit standing and the credit standing of our counterparties, and by considering any credit enhancements (e.g., collateral). Included in our valuation, and based on current market conditions, is a valuation adjustment for counterparty default derived from market data such as the price of credit default swaps, bond yields, and credit ratings. No material gains or losses related to valuation adjustments for counterparty default risk were recorded at Ameren, Ameren Missouri, or Ameren Illinois in the three months ended March 31, 2021 or 2020. At March 31, 2021, and December 31, 2020, the counterparty default risk valuation adjustment related to derivative contracts was immaterial for Ameren, Ameren Missouri, and Ameren Illinois.

The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of March 31, 2021, and December 31, 2020:

		March 31, 2021									December 31, 2020
		Level 1		Level 2		Level 3		Total			Level 1		Level 2		Level 3		Total
Assets:
Ameren Missouri
	Derivative assets – commodity contracts:
	Fuel oils	$	4	$	—	$	1	$	5		$	—	$	—	$	2	$	2
	Natural gas	—		4		—		4			—		3		—		3
	Power	2		—		3		5			2		—		5		7
	Total derivative assets – commodity contracts	$	6	$	4	$	4	$	14		$	2	$	3	$	7	$	12
	Nuclear decommissioning trust fund:
	Equity securities:
	U.S. large capitalization	$	679	$	—	$	—	$	679		$	680	$	—	$	—	$	680
	Debt securities:
	U.S. Treasury and agency securities	—		133		—		133			—		115		—		115
	Corporate bonds	—		128		—		128			—		115		—		115
	Other	—		63		—		63			—		67		—		67
	Total nuclear decommissioning trust fund	$	679	$	324	$	—	$	1,003	(a)	$	680	$	297	$	—	$	977	(a)
	Total Ameren Missouri	$	685	$	328	$	4	$	1,017		$	682	$	300	$	7	$	989
Ameren Illinois
	Derivative assets – commodity contracts:
	Natural gas	$	—	$	10	$	4	$	14		$	—	$	6	$	4	$	10
Ameren
	Derivative assets – commodity contracts(b)	$	6	$	14	$	8	$	28		$	2	$	9	$	11	$	22
	Nuclear decommissioning trust fund(c)	679		324		—		1,003		(a)	680		297		—		977		(a)
	Total Ameren	$	685	$	338	$	8	$	1,031		$	682	$	306	$	11	$	999
Liabilities:
Ameren Missouri
	Derivative liabilities – commodity contracts:
	Fuel oils	$	1	$	—	$	2	$	3		$	6	$	—	$	3	$	9
	Natural gas	—		—		—		—			—		1		—		1
	Power	8		—		6		14			8		—		3		11
	Total Ameren Missouri	$	9	$	—	$	8	$	17		$	14	$	1	$	6	$	21
Ameren Illinois
	Derivative liabilities – commodity contracts:
	Natural gas	$	—	$	—	$	—	$	—		$	—	$	1	$	1	$	2
	Power	—		—		185		185			—		—		198		198
	Total Ameren Illinois	$	—	$	—	$	185	$	185		$	—	$	1	$	199	$	200
Ameren
	Derivative liabilities – commodity contracts(b)	$	9	$	—	$	193	$	202		$	14	$	2	$	205	$	221

(a)Balance excludes $7 million and $5 million of cash and cash equivalents, receivables, payables, and accrued income, net, for March 31, 2021, and December 31, 2020, respectively.

(b)See the Ameren Missouri and Ameren Illinois sections of the table for a breakout of the fair value of Ameren’s derivative assets and liabilities by type of commodity.

(c)See the Ameren Missouri section of the table for a breakout of the fair value of Ameren's nuclear decommissioning trust fund by investment type.

Level 3 fuel oils and natural gas derivative contract assets and liabilities measured at fair value on a recurring basis were immaterial for all periods presented. The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the three months ended March 31, 2021 and 2020:

	2021						2020
	Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois		Ameren
For the three months ended March 31:
Beginning balance at January 1	$	2	$	(198)	$	(196)	$	13	$	(224)	$	(211)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities	(5)		9		4		11		(21)		(10)
Settlements	—		4		4		(7)		4		(3)
Ending balance at March 31	$	(3)	$	(185)	$	(188)	$	17	$	(241)	$	(224)
Change in unrealized gains/(losses) related to assets/liabilities held at March 31	$	(3)	$	9	$	6	$	10	$	(21)	$	(11)

All gains or losses related to our Level 3 derivative commodity contracts are expected to be recovered or returned through customer rates; therefore, there is no impact to either net income or other comprehensive income resulting from changes in the fair value of these instruments.

The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of March 31, 2021, and December 31, 2020:

			Fair Value						Weighted Average(b)
	Commodity		Assets		Liabilities	Valuation Technique(s)	Unobservable Input(a)	Range
2021	Power(c)	$	3	$	(191)	Discounted cash flow	Average forward peak and off-peak pricing – forwards/swaps ($/MWh)	23 – 40	29
							Nodal basis ($/MWh)	(5) – 0	(1)
							Trend rate (%)	2 – 5	3
2020	Power(c)	$	5	$	(201)	Discounted cash flow	Average forward peak and off-peak pricing – forwards/swaps ($/MWh)	23 – 37	29
							Nodal basis ($/MWh)	(6) – 0	(2)
							Trend rate (%)	2 – 6	3

(a)Generally, significant increases (decreases) in these inputs in isolation would result in a significantly higher (lower) fair value measurement.

(b)Unobservable inputs were weighted by relative fair value.

(c)Valuations through 2029 use visible forward prices adjusted for nodal-to-hub basis differentials. Valuations beyond 2029 use a trend rate factor and are similarly adjusted for nodal-to-hub basis differentials.

The following table sets forth the carrying amount and, by level within the fair value hierarchy, the fair value of financial assets and liabilities disclosed, but not recorded, at fair value as of March 31, 2021, and December 31, 2020:

	Carrying Amount			Fair Value
				Level 1		Level 2		Level 3			Total
	March 31, 2021
Ameren:
Cash, cash equivalents, and restricted cash	$	172		$	172	$	—	$	—		$	172
Investments in industrial development revenue bonds(a)	256			—		256		—			256
Short-term debt	889			—		889		—			889
Long-term debt (including current portion)(a)	11,535		(b)	—		12,233		507		(c)	12,740
Ameren Missouri:
Cash, cash equivalents, and restricted cash	$	12		$	12	$	—	$	—		$	12
Investments in industrial development revenue bonds(a)	256			—		256		—			256
Short-term debt	204			—		204		—			204
Long-term debt (including current portion)(a)	5,104		(b)	—		5,685		—			5,685
Ameren Illinois:
Cash, cash equivalents, and restricted cash	$	149		$	149	$	—	$	—		$	149
Short-term debt	323			—		323		—			323
Long-term debt (including current portion)	3,947		(b)	—		4,401		—			4,401
	December 31, 2020
Ameren:
Cash, cash equivalents, and restricted cash	$	301		$	301	$	—	$	—		$	301
Investments in industrial development revenue bonds(a)	256			—		256		—			256
Short-term debt	490			—		490		—			490
Long-term debt (including current portion)(a)	11,086		(b)	—		12,778		537		(c)	13,315
Ameren Missouri:
Cash, cash equivalents, and restricted cash	$	145		$	145	$	—	$	—		$	145
Advances to money pool	139			—		139		—			139
Investments in industrial development revenue bonds(a)	256			—		256		—			256
Long-term debt (including current portion)(a)	5,104		(b)	—		6,160		—			6,160
Ameren Illinois:
Cash, cash equivalents, and restricted cash	$	147		$	147	$	—	$	—		$	147
Borrowings from money pool	19			—		19		—			19
Long-term debt (including current portion)	3,946		(b)	—		4,822		—			4,822

(a)Ameren and Ameren Missouri have investments in industrial development revenue bonds, classified as held-to-maturity and recorded in “Other Assets,” that are equal to the finance obligations for the Peno Creek and Audrain CT energy centers. As of March 31, 2021, and December 31, 2020, the carrying amount of both the investments in industrial development revenue bonds and the finance obligations approximated fair value.

(b)Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $86 million, $36 million, and $36 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of March 31, 2021. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $84 million, $36 million, and $36 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2020.

(c)The Level 3 fair value amount consists of ATXI’s senior unsecured notes.

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Related Party Transactions

3 Months Ended

Mar. 31, 2021

Related Party Transactions [Abstract]

RELATED PARTY TRANSACTIONS

RELATED-PARTY TRANSACTIONS

In the ordinary course of business, Ameren Missouri and Ameren Illinois have engaged in, and may in the future engage in, affiliate transactions. These transactions primarily consist of natural gas and power purchases and sales, services received or rendered, and borrowings and lendings. Transactions between Ameren’s subsidiaries are reported as affiliate transactions on their individual financial statements, but those transactions are eliminated in consolidation for Ameren’s consolidated financial statements. For a discussion of material related-party agreements and money pool arrangements, see Note 13 – Related-party Transactions and Note 4 – Short-term Debt and Liquidity under Part II, Item 8, of the Form 10-K. For information Ameren Missouri’s and Ameren Illinois’ capital contributions, see Note 4 – Long-term Debt and Equity Financings.

Electric Power Supply Agreement

In April 2021, Ameren Illinois conducted a procurement event, administered by the IPA, to purchase energy products. Ameren Missouri was among the winning suppliers in this event. As a result, in April 2021, Ameren Missouri and Ameren Illinois entered into an energy product agreement by which Ameren Missouri agreed to sell and Ameren Illinois agreed to purchase, 33,600 MWhs at an average price of $34 per MWh during the period of July 2022 through November 2022.

Tax Allocation Agreement

See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of the Form 10-K for a discussion of the tax allocation agreement. The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of March 31, 2021, and December 31, 2020:

	March 31, 2021				December 31, 2020
	Ameren Missouri		Ameren Illinois		Ameren Missouri		Ameren Illinois
Income taxes payable to parent(a)	$	—	$	6	$	—	$	6
Income taxes receivable from parent(b)	14		18		9		15

(a)Included in “Accounts payable – affiliates” on the balance sheet.

(b)Included in “Accounts receivable – affiliates” on the balance sheet.

Effects of Related-party Transactions on the Statement of Income

The following table presents the effect on Ameren Missouri and Ameren Illinois of related-party transactions for the three months ended March 31, 2021 and 2020:

				Three Months
Agreement	Income Statement Line Item			Ameren Missouri		Ameren Illinois
Ameren Missouri power supply	Operating Revenues	2021	$	2	$	(a)
agreements with Ameren Illinois		2020		3		(a)
Ameren Missouri and Ameren Illinois	Operating Revenues	2021	$	7	$	(b)
rent and facility services		2020		7		1
Ameren Missouri and Ameren Illinois miscellaneous	Operating Revenues	2021	$	(b)	$	(b)
support services and services provided to ATXI		2020		(b)		(b)
Total Operating Revenues		2021	$	9	$	(b)
		2020		10		1
Ameren Illinois power supply	Purchased Power	2021	$	(a)	$	2
agreements with Ameren Missouri		2020		(a)		3
Ameren Missouri and Ameren Illinois	Purchased Power	2021	$	1	$	(b)
transmission services from ATXI		2020		(a)		(b)
Total Purchased Power		2021	$	1	$	2
		2020		(a)		3
Ameren Missouri and Ameren Illinois	Other Operations and Maintenance	2021	$	(b)	$	1
rent and facility services		2020		(b)		1
Ameren Services support services	Other Operations and Maintenance	2021	$	35	$	33
agreement		2020		35		33
Total Other Operations and		2021	$	35	$	34
Maintenance		2020		35		34
Money pool borrowings (advances)	(Interest Charges)/Other Income, Net	2021	$	(b)	$	(b)
		2020		(b)		(b)

(a)Not applicable.

(b)Amount less than $1 million.

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Commitments And Contingencies

3 Months Ended

Mar. 31, 2021

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

COMMITMENTS AND CONTINGENCIES

We are involved in legal, tax, and regulatory proceedings before various courts, regulatory commissions, authorities, and governmental agencies with respect to matters that arise in the ordinary course of business, some of which involve substantial amounts of money. We believe that the final disposition of these proceedings, except as otherwise disclosed in the notes to our financial statements in this report and in the Form 10-K, will not have a material adverse effect on our results of operations, financial position, or liquidity.

Reference is made to Note 1 – Summary of Significant Accounting Policies, Note 2 – Rate and Regulatory Matters, Note 9 – Callaway Energy Center, Note 13 – Related-party Transactions, and Note 14 – Commitments and Contingencies under Part II, Item 8, of the Form 10-K. See also Note 1 – Summary of Significant Accounting Policies, Note 2 – Rate and Regulatory Matters, Note 8 – Related-party Transactions, and Note 10 – Callaway Energy Center of this report.

Environmental Matters

Our electric and gas generation, transmission, distribution and gas storage operations must comply with a variety of environmental statutory and regulatory requirements, including permitting programs implemented via federal, state, and local authorities. Depending upon the specific business activity of the facility, such laws address air emissions; discharges to water bodies; the storage, handling, and disposal of hazardous substances and waste materials; siting and land use requirements; and potential ecological impacts. Complex and lengthy processes are required to obtain and renew approvals, permits, and licenses for new, existing, or modified facilities. Additionally, the use and handling of various chemicals or hazardous materials require release prevention plans and emergency response procedures. We employ dedicated personnel knowledgeable in environmental matters to oversee our business activities’ compliance with regulatory requirements.

Environmental regulations have a significant impact on the electric utility industry and compliance with these regulations could be costly for Ameren Missouri, which operates coal-fired power plants. Clean Air Act regulations that apply to the electric utility industry include the NSPS, the CSAPR, the MATS, and the National Ambient Air Quality Standards, which are subject to periodic review for certain pollutants. Collectively, these regulations cover a variety of pollutants, such as SO2, particulate matter, NOx, mercury, toxic metals, and acid gases, and CO2 emissions from new power plants. Clean Water Act regulations applicable to coal-fired power plants govern both intake and discharges of water and require evaluation of the ecological and biological impact of our operations and could require modifications to water intake structures or more stringent limitations on wastewater discharges. Depending upon the scope of modifications ultimately required by state regulators, these capital expenditures could be significant. The management and disposal of coal ash is regulated under the Resource Conservation and Recovery Act and the CCR rule and requires the closure of our surface impoundments at Ameren Missouri’s coal-fired energy centers. The individual or combined effects of existing and new environmental regulations could result in significant capital expenditures, increased operating costs, or the closure or alteration of operations at some of Ameren Missouri’s energy centers. Ameren and Ameren Missouri expect that such compliance costs would be recoverable through rates, subject to MoPSC prudence review, but the timing of costs and their recovery could be subject to regulatory lag.

Ameren and Ameren Missouri estimate that they will need to make capital expenditures of $175 million to $225 million from 2021 through 2025 in order to comply with existing environmental regulations. Additional environmental controls beyond 2025 could be required. This estimate of capital expenditures includes ash pond closure and corrective action measures required by the CCR regulations, potential modifications to cooling water intake structures at existing power plants under Clean Water Act rules, and by effluent limitation guidelines applicable to steam electric generating units, all of which are discussed below. This estimate does not include capital expenditures that may be required as a result of the NSR and Clean Air Act litigation discussed below. Ameren Missouri’s current plan for compliance with existing air emission regulations includes burning low-sulfur coal and installing new or optimizing existing air pollution control equipment. The actual amount of capital expenditures required to comply with existing environmental regulations may vary substantially from the above estimates because of uncertainty as to future permitting requirements made by state regulators and the EPA, potential revisions to regulatory obligations, and the cost of potential compliance strategies, among other things.

The following sections describe the more significant environmental laws and rules and environmental enforcement and remediation matters that affect or could affect our operations. The EPA has initiated an administrative review of several regulations and proposed amendments to regulations and guidelines, including to the effluent limitation guidelines and the CCR Rule, which could ultimately result in the revision of all or part of such rules.

Clean Air Act

Federal and state laws, including CSAPR, regulate emissions of SO2 and NOx through the reduction of emissions at their source and the use and retirement of emission allowances. CSAPR is implemented through a series of phases, and the second phase became effective in 2017. Additional emission reduction requirements may apply in subsequent years. Ameren Missouri complies with current CSAPR requirements by minimizing emissions through the use of low-sulfur coal, operation of two scrubbers at its Sioux Energy Center, and optimization of other existing air pollution control equipment. Ameren Missouri could incur additional costs to lower its emissions at one or more of its energy centers to comply additional CSAPR requirements in future years. These additional costs for compliance are expected to be recovered from customers through the FAC or higher base rates.

CO2 Emissions Standards

The EPA’s Affordable Clean Energy Rule repealed the Clean Power Plan and replaced it with a new rule that established emission guidelines for states to follow in developing plans to limit CO2 emissions and identified certain efficiency measures as the best system of emission reduction for coal-fired electric generating units. In January 2021, the United States Court of Appeals for the District of Columbia Circuit vacated the Affordable Clean Energy Rule, and ruled that the EPA had the discretion to consider emission reduction measures that include efficiency measures and generation shifting to lower carbon emissions. The United States Supreme Court has extended the deadline for seeking review, and a decision on whether the Supreme Court will review the circuit court's ruling could occur in fall 2021. Regardless of the outcome of those legal challenges, the EPA is likely to develop new regulations to address carbon emissions from coal and natural gas electric generating units. At this time, Ameren Missouri cannot predict the outcome of legal challenges to the vacated Affordable Clean

Energy Rule or future rulemakings. As such, the impact on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri is uncertain.

NSR and Clean Air Litigation

In January 2011, the Department of Justice, on behalf of the EPA, filed a complaint against Ameren Missouri in the United States District Court for the Eastern District of Missouri alleging that in performing projects at its coal-fired Rush Island Energy Center in 2007 and 2010, Ameren Missouri violated provisions of the Clean Air Act and Missouri law. In January 2017, the district court issued a liability ruling and, in September 2019, entered a final order that required Ameren Missouri to install a flue gas desulfurization system at the Rush Island Energy Center and a dry sorbent injection system at the Labadie Energy Center. There were no fines in the order as the Department of Justice previously dismissed claims for penalties. The district court stayed implementation of the majority of the requirements of its order while the case is under appeal to the United States Court of Appeals for the Eighth Circuit. In December 2020, the court of appeals heard oral arguments presented by the parties. The court is under no deadline to issue a ruling in this case and Ameren Missouri is unable to predict the ultimate resolution of this matter. Ameren Missouri expects a ruling by the court of appeals during 2021.

The ultimate resolution of this matter could have a material adverse effect on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri. Among other things and subject to economic and regulatory considerations, resolution of this matter could result in increased capital expenditures for the installation of air pollution control equipment, as well as increased operations and maintenance expenses. Based upon engineering studies from October 2019, capital expenditures to comply with the district court’s order for installation of a flue gas desulfurization system at the Rush Island Energy Center are estimated at approximately $1 billion. Further, the flue gas desulfurization system would result in additional operation and maintenance expenses of $30 million to $50 million annually for the life of the energy center. Engineering studies required to develop estimated capital expenditures and estimated additional operation and maintenance expenses for the Labadie Energy Center to comply with the district court’s order will not be undertaken while the case is under appeal. As a result of the district court’s stay, Ameren Missouri does not expect to make significant capital expenditures or incur operations and maintenance expenses related to the district court’s order while the case is under appeal.

Clean Water Act

The EPA’s Section 316(b) Rule requires power plant operators to evaluate cooling water intake structures and identify measures for reducing the number of aquatic organisms impinged on a power plant’s cooling water intake screens or entrained through the plant’s cooling water system. All of Ameren Missouri’s coal-fired and nuclear energy centers are subject to the cooling water intake structures rule. Requirements of the rule are implemented by state regulators through the permit renewal process of each energy center’s water discharge permit, which is expected to be completed by 2023.

In 2015, the EPA issued a rule to revise the effluent limitation guidelines applicable to steam electric generating units. These guidelines established national standards for water discharges, prohibits effluent discharges of certain waste streams, and imposes more stringent limitations on certain water discharges from power plants. To meet the requirements of the guidelines, Ameren Missouri installed dry ash handling systems and in 2020 completed construction of wastewater treatment facilities at three of its four coal-fired energy centers. The Meramec Energy Center is scheduled to close permanently in 2022, and as a result, does not require new wastewater and dry ash handling systems. Estimated capital expenditures to complete these projects are included in the CCR management compliance plan, discussed below.

CCR Management

The EPA’s CCR rule establishes requirements for the management and disposal of CCR from coal-fired power plants and will result in the closure of surface impoundments at Ameren Missouri’s energy centers. Ameren Missouri is in the process of closing surface impoundments at all of its facilities, and is scheduled to complete the last of such closures in 2023. The EPA has issued a series of revisions to the CCR rule; however, none of those revisions is expected to materially impact our closure schedule. Ameren and Ameren Missouri have AROs of $103 million recorded on their respective balance sheets as of March 31, 2021, associated with CCR storage facilities. Ameren Missouri estimates it will need to make capital expenditures of $75 million to $100 million from 2021 through 2025 to implement its CCR management compliance plan, which includes installation of groundwater monitoring equipment and water treatment facilities.

Remediation

The Ameren Companies are involved in a number of remediation actions to clean up sites impacted by the use or disposal of materials containing hazardous substances. Federal and state laws can require responsible parties to fund remediation regardless of their degree of fault, the legality of original disposal, or the ownership of a disposal site.

As of March 31, 2021, Ameren Illinois has remediated the majority of the 44 former MGP sites in Illinois and could substantially conclude remediation efforts at the remaining sites by 2023. The ICC allows Ameren Illinois to recover such remediation and related litigation costs from its electric and natural gas utility customers through environmental cost riders that are subject to annual prudence review by the ICC. As

of March 31, 2021, Ameren Illinois estimated the remaining obligation related to these former MGP sites at $90 million to $150 million. Ameren and Ameren Illinois recorded a liability of $90 million to represent the estimated minimum obligation for these sites, as no other amount within the range was a better estimate.

The scope of the remediation activities at these former MGP sites may increase as remediation efforts continue. Considerable uncertainty remains in these estimates because many site-specific factors can influence the ultimate actual costs, including unanticipated underground structures, the degree to which groundwater is encountered, regulatory changes, local ordinances, and site accessibility. The actual costs and timing of completion may vary substantially from these estimates.

Our operations or those of our predecessor companies involve the use of, disposal of, and, in appropriate circumstances, the cleanup of substances regulated under environmental laws. We are unable to determine whether such historical practices will result in future environmental commitments or will affect our results of operations, financial position, or liquidity.

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Callaway Energy Center

3 Months Ended

Mar. 31, 2021

Nuclear Waste Matters [Abstract]

CALLAWAY ENERGY CENTER

CALLAWAY ENERGY CENTER

See Note 9 – Callaway Energy Center under Part II, Item 8, of the Form 10-K for information regarding spent nuclear fuel recovery, recovery of decommissioning costs, and the nuclear decommissioning trust fund. The fair value of the trust fund for Ameren Missouri’s Callaway Energy Center is reported as “Nuclear decommissioning trust fund” in Ameren’s and Ameren Missouri’s balance sheets. This amount is legally restricted and may be used only to fund the costs of nuclear decommissioning. Changes in the fair value of the trust fund are recorded as an increase or decrease to the nuclear decommissioning trust fund, with an offsetting adjustment to the related regulatory liability. Ameren and Ameren Missouri have recorded an ARO for the Callaway Energy Center decommissioning costs at fair value, which represents the present value of estimated future cash outflows. Annual decommissioning costs of $7 million are included in the costs used to establish electric rates for Ameren Missouri’s customers. Every three years, the MoPSC requires Ameren Missouri to file an updated cost study and funding analysis for decommissioning its Callaway Energy Center. An updated cost study and funding analysis was filed with the MoPSC in November 2020 and reflected within the ARO. In February 2021, the MoPSC approved no change in electric rates for decommissioning costs based on Ameren Missouri’s updated cost study funding analysis. See Note 13 – Supplemental Information for more information on Ameren Missouri’s AROs.

Maintenance Outage

During its return to full power after the completion of the last refueling and maintenance outage in late December 2020, the Callaway Energy Center experienced a non-nuclear operating issue related to its generator. A thorough investigation of this matter was conducted. Work continues to replace certain key components of the generator in order to return the energy center to service. Ameren Missouri expects generator repairs of approximately $65 million, which are expected to be largely capital expenditures. Due to the long lead time for the manufacture, repair, and installation of the components, the energy center is expected to return to service in July 2021. In April 2021, Ameren Missouri’s insurance claims were accepted by NEIL, which are expected to cover a significant portion of the capital expenditures and replacement power costs. Replacement power costs of up to $4.5 million weekly are covered by insurance after March 17, 2021. Insurance recoveries related to replacement power costs will be reflected in electric operating revenues and included in net energy costs under the FAC. Insurance recoveries related to the capital expenditures will be reflected as a reduction to property, plant, and equipment. Ameren Missouri continues to review other legal remedies available.

Insurance

The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at April 1, 2021:

Type and Source of Coverage	Most Recent Renewal Date	Maximum Coverages			Maximum Assessments for Single Incidents
Public liability and nuclear worker liability:
American Nuclear Insurers	January 1, 2021	$	450		$	—
Pool participation	(a)	13,210		(a)	138		(b)
		$	13,660	(c)	$	138
Property damage:
NEIL and EMANI	April 1, 2021	$	3,200	(d)	$	25	(e)
Replacement power:
NEIL	April 1, 2021	$	490	(f)	$	7	(e)

(a)Provided through mandatory participation in an industrywide retrospective premium assessment program. The maximum coverage available is dependent on the number of United States commercial reactors participating in the program.

(b)Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $450 million in the event of an incident at any licensed United States commercial reactor, payable at $21 million per year.

(c)Limit of liability for each incident under the Price-Anderson liability provisions of the Atomic Energy Act of 1954, as amended. This limit is subject to change to account for the effects of inflation and changes in the number of licensed power reactors.

(d)NEIL provides $2.7 billion in property damage, stabilization, decontamination, and premature decommissioning insurance for radiation events and $2.3 billion in property damage insurance for nonradiation events. EMANI provides $490 million in property damage insurance for both radiation and nonradiation events.

(e)All NEIL-insured plants could be subject to assessments should losses exceed the accumulated funds from NEIL.

(f)Provides replacement power cost insurance in the event of a prolonged accidental outage. Weekly indemnity up to $4.5 million for 52 weeks, which commences after the first 12 weeks of an outage, plus up to $3.6 million per week for a minimum of 71 weeks thereafter for a total not exceeding the policy limit of $490 million. Nonradiation events are limited to $328 million.

The Price-Anderson Act is a federal law that limits the liability for claims from an incident involving any licensed United States commercial nuclear energy center. The limit is based on the number of licensed reactors. The limit of liability and the maximum potential annual payments are adjusted at least every five years for inflation to reflect changes in the Consumer Price Index. The most recent five-year inflationary adjustment became effective in November 2018. Owners of a nuclear reactor cover this exposure through a combination of private insurance and mandatory participation in a financial protection pool, as established by the Price-Anderson Act.

Losses resulting from terrorist attacks on nuclear facilities insured by NEIL are subject to industrywide aggregates, such that terrorist acts against one or more commercial nuclear power plants within a stated time period would be treated as a single event, and the owners of the nuclear power plants would share the limit of liability. NEIL policies have an aggregate limit of $3.2 billion within a 12-month period for radiation events, or $1.8 billion for events not involving radiation contamination, resulting from terrorist attacks. The EMANI policies are not subject to industrywide aggregates in the event of terrorist attacks on nuclear facilities.

If losses from a nuclear incident at the Callaway Energy Center exceed the limits of, or are not covered by insurance, or if coverage is unavailable, Ameren Missouri is at risk for any uninsured losses. If a serious nuclear incident were to occur, it could have a material adverse effect on Ameren’s and Ameren Missouri’s results of operations, financial position, or liquidity.

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Retirement Benefits

3 Months Ended

Mar. 31, 2021

Retirement Benefits [Abstract]

RETIREMENT BENEFITS

RETIREMENT BENEFITS

The following table presents the components of the net periodic benefit cost (income) incurred for Ameren’s pension and postretirement benefit plans for the three months ended March 31, 2021 and 2020:

	Pension Benefits				Postretirement Benefits
	Three Months				Three Months
	2021		2020		2021		2020
Service cost(a)	$	33	$	27	$	6	$	4
Non-service cost components:
Interest cost	38		43		8		10
Expected return on plan assets	(75)		(73)		(20)		(20)
Amortization of:
Prior service benefit	—		—		(1)		(1)
Actuarial loss (gain)	17		14		(1)		(2)
Total non-service cost components(b)	$	(20)	$	(16)	$	(14)	$	(13)
Net periodic benefit cost (income)	$	13	$	11	$	(8)	$	(9)

(a)Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income.

(b)Non-service cost components are reflected in “Other Income, Net” on Ameren’s statement of income. See Note 5 – Other Income, Net, for additional information.

Ameren Missouri and Ameren Illinois are responsible for their respective share of Ameren’s pension and other postretirement costs. The following table presents the respective share of net periodic pension and other postretirement benefit costs (income) incurred for the three months ended March 31, 2021 and 2020:

	Pension Benefits				Postretirement Benefits
	Three Months				Three Months
	2021		2020		2021		2020
Ameren Missouri(a)	$	6	$	4	$	(1)	$	(1)
Ameren Illinois	8		7		(7)		(8)
Other	(1)		—		—		—
Ameren(a)	$	13	$	11	$	(8)	$	(9)

(a)Does not include the impact of the regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates.

Funding

Based on its assumptions at March 31, 2021, its investment performance in 2021, and its pension funding policy, the estimated aggregate contributions through 2025 has not changed from the $60 million expected aggregate contributions at December 31, 2020.

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Income Taxes

3 Months Ended

Mar. 31, 2021

Income Tax Disclosure [Abstract]

Income Taxes

INCOME TAXES

The following table presents a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the three months ended March 31, 2021 and 2020:

	Ameren		Ameren Missouri		Ameren Illinois
	2021	2020	2021	2020	2021	2020
Three Months
Federal statutory corporate income tax rate:	21%	21%	21%	21%	21%	21%
Increases (decreases) from:
Amortization of deferred investment tax credit	(1)	—	(1)	(1)	—	—
Amortization of excess deferred taxes	(9)	(9)	(17)	(15)	(2)	(3)
Depreciation differences	—	(1)	1	—	(1)	(1)
Renewable and other tax credits	(6)	—	(11)	—	—	—
State tax	6	6	3	3	7	7
Stock-based compensation	(1)	(5)	—	—	—	—
Effective income tax rate	10%	12%	(4)%	8%	25%	24%

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Supplemental Information

3 Months Ended

Mar. 31, 2021

Supplemental Information [Abstract]

Supplemental Information

SUPPLEMENTAL INFORMATION

Cash, Cash Equivalents, and Restricted Cash

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows as of March 31, 2021, and December 31, 2020:

	March 31, 2021						December 31, 2020
	Ameren		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois
Cash and cash equivalents	$	6	$	1	$	—	$	139	$	136	$	—
Restricted cash	134		—		125		17		—		6
Restricted cash included in “Other current assets”	—		3		—		—		5		—
Restricted cash included in “Other assets”	24		—		24		141		—		141
Restricted cash included in “Nuclear decommissioning trust fund”	8		8		—		4		4		—
Total cash, cash equivalents, and restricted cash	$	172	$	12	$	149	$	301	$	145	$	147

Restricted cash included in “Other current assets” primarily represents funds held by an irrevocable Voluntary Employee Beneficiary Association (VEBA) trust, which provides health care benefits for active employees. As of December 31, 2020, restricted cash included in “Other assets” on Ameren’s and Ameren Illinois’ balance sheets primarily represents amounts collected under a cost recovery rider restricted for use in the procurement of renewable energy credits and amounts in a trust fund restricted for the use of funding certain asbestos-related claims. As of March 31, 2021, the amounts collected under a cost recovery rider restricted for use in Ameren Illinois’ procurement of renewable energy credits was reclassified to current as the amount is expected to be refunded to customers within a year.

Accounts Receivable

“Accounts receivable – trade” on Ameren’s and Ameren Illinois’ balance sheets include certain receivables purchased at a discount from alternative retail electric suppliers that elect to participate in the utility consolidated billing program. At March 31, 2021, and December 31, 2020, “Other current liabilities” on Ameren’s and Ameren Illinois’ balance sheets included payables for purchased receivables of $31 million and $28 million, respectively.

The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the three months ended March 31, 2021 and 2020:

	Three Months
	2021		2020
Ameren:
Beginning of period	$	50	$	17
Bad debt expense	4		3
Net write-offs	(7)		(1)
End of period	$	47	$	19
Ameren Missouri:
Beginning of period	$	16	$	7
Bad debt expense	1		2
Net write-offs	(2)		(1)
End of period	$	15	$	8
Ameren Illinois:(a)
Beginning of Period	$	34	$	10
Bad debt expense	3		1
Net write-offs	(5)		—
End of Period	$	32	$	11

(a)Ameren Illinois has rate-adjustment mechanisms that allow it to recover the difference between its actual net bad debt write-offs under GAAP, including those associated with receivables purchased from alternative retail electric suppliers, and the amount of net bad debt write-offs included in its base rates.

Net write-offs increased for the three months ended March 31, 2021, compared with the year-ago period, due to the resumption of disconnection activities for nonpayment. See Note 2 – Rate and Regulatory Matters for additional information.

Supplemental Cash Flow Information

The following table provides noncash financing and investing activity excluded from the statements of cash flows for the three months ended March 31, 2021 and 2020:

	March 31, 2021						March 31, 2020
	Ameren		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois
Investing
Accrued capital expenditures, including wind generation expenditures	$	271	$	141	$	139	$	235	$	97	$	127
Accrued nuclear fuel expenditures	—		—		—		7		7		—
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund	22		22		—		(111)		(111)		—
Financing
Issuance of common stock for stock-based compensation	33		—		—		38		—		—

Asset Retirement Obligations

The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the three months ended March 31, 2021:

	Ameren Missouri			Ameren Illinois			Ameren
Balance at December 31, 2020	$	751		$	5	(a)	$	756	(b)
Liabilities incurred (c)	10			—			10
Liabilities settled	(3)			—			(3)
Accretion	8		(d)	—			8		(d)
Change in estimates	(7)		(e)	—			(7)		(e)
Balance at March 31, 2021	$	759		$	5	(a)	$	764	(b)

(a)Included in “Other deferred credits and liabilities” on the balance sheet.

(b)Balance included $59 million and $60 million in “Other current liabilities” on the balance sheet as of March 31, 2021, and December 31, 2020, respectively.

(c)In the first quarter of 2021, Ameren Missouri recorded an ARO related to the decommissioning for the Atchison Renewable Energy Center.

(d)Accretion expense attributable to Ameren Missouri was recorded as a decrease to regulatory liabilities.

(e)Ameren Missouri changed its fair value estimate primarily due to a decrease in the cost estimate for closure of certain CCR storage facilities.

Stock-based Compensation

On January 1, 2021, Ameren granted 293,058 performance share units with a grant date fair value of $25 million and 125,562 restricted share units with a grant date fair value of $10 million. Awards vest approximately 38 months after the grant date or on a pro-rata basis upon death or eligible retirement. The performance share units vest based on the achievement of certain specified market performance measures (251,177 performance share units) or based on the achievement of renewable generation and energy storage installation targets (41,881 performance share units). The exact number of shares issued pursuant to a performance share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the performance goals.

For the three months ended March 31, 2021 and 2020, excess tax benefits associated with the settlement of stock-based compensation awards reduced income tax expense by $5 million and $8 million, respectively.

Deferred Compensation

As of both March 31, 2021, and December 31, 2020, the present value of benefits to be paid for deferred compensation obligations was $90 million, which was primarily reflected in “Other deferred credits and liabilities” on Ameren's consolidated balance sheet.

Operating Revenues

As of March 31, 2021 and 2020, our remaining performance obligations for contracts with a term greater than one year were immaterial. The Ameren Companies elected not to disclose the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied as of the end of the reporting period for contracts with an initial expected term of one year or less.

See Note 14 – Segment Information for disaggregated revenue information.

Excise Taxes

Ameren Missouri and Ameren Illinois collect from their customers excise taxes, including municipal and state excise taxes and gross receipts taxes that are levied on the sale or distribution of natural gas and electricity. The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the three months ended March 31, 2021 and 2020:

	Three Months
	2021		2020
Ameren Missouri	$	31	$	30
Ameren Illinois	39		35
Ameren	$	70	$	65

Earnings per Share

The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three months ended March 31, 2021 and 2020:

	Three Months
	2021	2020
Weighted-average Common Shares Outstanding – Basic	254.4	246.4
Assumed settlement of performance share units and restricted stock units	1.5	1.1
Dilutive effect of forward sale agreement	—	0.6
Weighted-average Common Shares Outstanding – Diluted(a)	255.9	248.1

(a)There were no potentially dilutive securities excluded from the earnings per diluted share calculations for the three months ended March 31, 2021 and 2020.

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Segment Information

3 Months Ended

Mar. 31, 2021

Segment Reporting [Abstract]

SEGMENT INFORMATION

SEGMENT INFORMATION

The following tables present revenues, net income (loss) attributable to common shareholders, and capital expenditures by segment at Ameren and Ameren Illinois for the three months ended March 31, 2021 and 2020. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount. For additional information about our segments, see Note 16 – Segment Information under Part II, Item 8, of the Form 10-K.

Ameren

	Ameren Missouri			Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission			Other		Intersegment Eliminations		Ameren
Three Months 2021:
External revenues	$	695		$	411	$	347	$	113		$	—	$	—	$	1,566
Intersegment revenues	9			—		—		17			—		(26)		—
Net income attributable to Ameren common shareholders	47			46		75		47		(a)	18		—		233
Capital expenditures	534		(b)	157		48		141			1		6		887		(b)
Three Months 2020:
External revenues	$	670		$	389	$	271	$	110		$	—	$	—	$	1,440
Intersegment revenues	10			1		—		13			—		(24)		—
Net income (loss) attributable to Ameren common shareholders	(10)			37		55		47		(a)	17		—		146
Capital expenditures	278			123		61		170			3		1		636

(a)Ameren Transmission earnings reflect an allocation of financing costs from Ameren (parent).

(b)Includes $193 million at Ameren and Ameren Missouri for wind generation expenditures for the three months ended March 31, 2021.

Ameren Illinois

	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Intersegment Eliminations		Ameren Illinois
Three Months 2021:
External revenues	$	411	$	347	$	65	$	—	$	823
Intersegment revenues	—		—		16		(16)		—
Net income available to common shareholder	46		75		28		—		149
Capital expenditures	157		48		132		—		337
Three Months 2020:
External revenues	$	390	$	271	$	62	$	—	$	723
Intersegment revenues	—		—		12		(12)		—
Net income available to common shareholder	37		55		28		—		120
Capital expenditures	123		61		140		—		324

The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three months ended March 31, 2021 and 2020. Economic factors affect the nature, timing, amount, and uncertainty of revenues and cash flows in a similar manner across customer classes. Revenues from alternative revenue programs have a similar distribution among customer classes as revenues from contracts with customers. Other revenues not associated with contracts with customers are presented in the Other customer classification, along with electric transmission and off-system revenues.

Ameren

	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Intersegment Eliminations		Ameren
Three Months 2021:
Residential	$	312	$	229	$	—	$	—	$	—	$	541
Commercial	216		132		—		—		—		348
Industrial	52		34		—		—		—		86
Other	61		16		—		130		(26)		181
Total electric revenues	$	641	$	411	$	—	$	130	$	(26)	$	1,156
Residential	$	34	$	—	$	251	$	—	$	—	$	285
Commercial	15		—		64		—		—		79
Industrial	1		—		14		—		—		15
Other	13		—		18		—		—		31
Total natural gas revenues	$	63	$	—	$	347	$	—	$	—	$	410
Total revenues(a)	$	704	$	411	$	347	$	130	$	(26)	$	1,566
Three Months 2020:
Residential	$	297	$	220	$	—	$	—	$	—	$	517
Commercial	221		126		—		—		—		347
Industrial	53		35		—		—		—		88
Other	60		9		—		123		(24)		168
Total electric revenues	$	631	$	390	$	—	$	123	$	(24)	$	1,120
Residential	$	33	$	—	$	213	$	—	$	—	$	246
Commercial	13		—		54		—		—		67
Industrial	1		—		3		—		—		4
Other	2		—		1		—		—		3
Total natural gas revenues	$	49	$	—	$	271	$	—	$	—	$	320
Total revenues(a)	$	680	$	390	$	271	$	123	$	(24)	$	1,440

(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three months ended March 31, 2021 and 2020:

	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Ameren
Three Months 2021:
Revenues from alternative revenue programs	$	(10)	$	61	$	3	$	(1)	$	53
Other revenues not from contracts with customers	(2)		3		1		—		2
Three Months 2020:
Revenues from alternative revenue programs	$	(3)	$	46	$	11	$	12	$	66
Other revenues not from contracts with customers	8		1		1		—		10

Ameren Illinois

	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Intersegment Eliminations		Ameren Illinois
Three Months 2021:
Residential	$	229	$	251	$	—	$	—	$	480
Commercial	132		64		—		—		196
Industrial	34		14		—		—		48
Other	16		18		81		(16)		99
Total revenues(a)	$	411	$	347	$	81	$	(16)	$	823
Three Months 2020:
Residential	$	220	$	213	$	—	$	—	$	433
Commercial	126		54		—		—		180
Industrial	35		3		—		—		38
Other	9		1		74		(12)		72
Total revenues(a)	$	390	$	271	$	74	$	(12)	$	723

(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three months ended March 31, 2021 and 2020:

	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Ameren Illinois
Three Months 2021:
Revenues from alternative revenue programs	$	61	$	3	$	(1)	$	63
Other revenues not from contracts with customers	3		1		—		4
Three Months 2020:
Revenues from alternative revenue programs	$	46	$	11	$	10	$	67
Other revenues not from contracts with customers	1		1		—		2

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Summary Of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2021

Accounting Policies [Abstract]

Nature of Operations

Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren has other subsidiaries that conduct other activities, such as providing shared services.

•Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri.

•Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois.

•ATXI operates a FERC rate-regulated electric transmission business in the MISO.

Consolidation

Ameren’s financial statements are prepared on a consolidated basis and therefore include the accounts of its majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Missouri and Ameren Illinois have no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated.Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair statement of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates. The results of operations of an interim period may not give a true indication of results that may be expected for a full year. These financial statements should be read in conjunction with the financial statements and accompanying notes included in the Form 10-K.

Consolidation, Variable Interest Entity, Policy

Variable Interest Entities

As of March 31, 2021, and December 31, 2020, Ameren had unconsolidated variable interests as a limited partner in various equity method investments, totaling $41 million and $37 million, respectively, included in “Other assets” on Ameren’s consolidated balance sheet. Ameren is not the primary beneficiary of these investments because it does not have the power to direct matters that most significantly affect the activities of these variable interest entities. As of March 31, 2021, the maximum exposure to loss related to these variable interests is limited to the investment in these partnerships of $41 million plus associated outstanding funding commitments of $33 million.

Derivatives, Policy

We use derivatives to manage the risk of changes in market prices for natural gas and power, as well as the risk of changes in rail transportation surcharges through fuel oil hedges. Such price fluctuations may cause the following:

•an unrealized appreciation or depreciation of our contracted commitments to purchase or sell when purchase or sale prices under the commitments are compared with current commodity prices;

•market values of natural gas inventories that differ from the cost of those commodities in inventory;

•actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays; and

•actual off-system sales revenues that differ from anticipated revenues

The derivatives that we use to hedge these risks are governed by our risk management policies for forward contracts, futures, options, and swaps. Our net positions are continually assessed within our structured hedging programs to determine whether new or offsetting transactions are required. The goal of the hedging program is generally to mitigate financial risks while ensuring that sufficient volumes are available to meet our requirements. Contracts we enter into as part of our risk management program may be settled financially, settled by physical delivery, or net settled with the counterparty.

The Ameren Companies elect to present the fair value amounts of derivative assets and derivative liabilities subject to an enforceable master netting arrangement or similar agreement at the gross amounts on the balance sheet.

Deferred Compensation

Deferred Compensation

As of both March 31, 2021, and December 31, 2020, the present value of benefits to be paid for deferred compensation obligations was $90 million, which was primarily reflected in “Other deferred credits and liabilities” on Ameren's consolidated balance sheet.

Revenue from Contract with Customer

Operating Revenues

As of March 31, 2021 and 2020, our remaining performance obligations for contracts with a term greater than one year were immaterial. The Ameren Companies elected not to disclose the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied as of the end of the reporting period for contracts with an initial expected term of one year or less.

See Note 14 – Segment Information for disaggregated revenue information.

Excise Taxes

Excise TaxesAmeren Missouri and Ameren Illinois collect from their customers excise taxes, including municipal and state excise taxes and gross receipts taxes that are levied on the sale or distribution of natural gas and electricity.

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Short-Term Debt and Liquidity (Tables)

3 Months Ended

Mar. 31, 2021

Debt Disclosure [Abstract]

Schedule of Short-term Debt

The following table presents commercial paper outstanding, net of issuance discounts, as of March 31, 2021, and December 31, 2020. There were no borrowings outstanding under the Credit Agreements as of March 31, 2021, or December 31, 2020.

	March 31, 2021		December 31, 2020
Ameren (parent)	$	362	$	490
Ameren Missouri	204		—
Ameren Illinois	323		—
Ameren consolidated	$	889	$	490

The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances and borrowings under the Credit Agreements in the aggregate for the three months ended March 31, 2021 and 2020:

	Ameren (parent)			Ameren Missouri				Ameren Illinois			Ameren Consolidated
2021
Average daily amount outstanding	$	454		$	99			$	96		$	649
Weighted-average interest rate	0.25		%	0.22		%		0.21		%	0.24		%
Peak amount outstanding during period(a)	$	650		$	206			$	353		$	916
Peak interest rate	0.33		%	0.25		%		0.25		%	0.33		%
2020
Average daily amount outstanding	$	157		$	395			$	76		$	628
Weighted-average interest rate	1.94		%	1.86		%		1.99		%	1.89		%
Peak amount outstanding during period(a)	$	425		$	573			$	150		$	908
Peak interest rate	3.30		%	5.05		%	(b)	3.40		%	5.05		%	(b)

(a)The timing of peak outstanding commercial paper issuances and borrowings under the Credit Agreements varies by company. Therefore, the sum of individual company peak amounts may not equal the Ameren consolidated peak for the period.

(b)Ameren’s and Ameren Missouri’s peak interest rate was affected by temporary disruptions in the commercial paper market in the first quarter of 2020.

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Other Income and Expenses (Tables)

3 Months Ended

Mar. 31, 2021

Other Nonoperating Income (Expense) [Abstract]

Other Income And Expenses

The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the three months ended March 31, 2021 and 2020:

	Three Months
	2021		2020
Ameren:
Allowance for equity funds used during construction	$	7	$	4
Interest income on industrial development revenue bonds	6		6
Other interest income	1		1
Non-service cost components of net periodic benefit income(a)	34		23
Miscellaneous income	4		2
Donations	(3)		(13)		(b)
Miscellaneous expense	(3)		(2)
Total Other Income, Net	$	46	$	21
Ameren Missouri:
Allowance for equity funds used during construction	$	4	$	2
Interest income on industrial development revenue bonds	6		6
Non-service cost components of net periodic benefit income(a)	14		5
Miscellaneous income	1		1
Donations	—		(8)		(b)
Miscellaneous expense	(2)		(2)
Total Other Income, Net	$	23	$	4
Ameren Illinois:
Allowance for equity funds used during construction	$	3	$	2
Interest income	1		1
Non-service cost components of net periodic benefit income	14		13
Miscellaneous income	—		1
Donations	(3)		(4)
Miscellaneous expense	(1)		(2)
Total Other Income, Net	$	14	$	11

(a)For the three months ended March 31, 2021 and 2020, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of less than $(1) million and $6 million, respectively, due to a regulatory tracking mechanism for the difference between the level of such costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates.

(b)Includes $8 million pursuant to Ameren Missouri’s March 2020 electric rate order. See Note 2 – Rate and Regulatory Matters under Part II, Item 8, in the Form 10-K for additional information.

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Derivative Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2021

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Open Gross Derivative Volumes By Commodity Type

The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of March 31, 2021, and December 31, 2020. As of March 31, 2021, these contracts extended through October 2023, October 2026, and May 2032 for fuel oils, natural gas and power, respectively.

	Quantity (in millions, except as indicated)
	March 31, 2021			December 31, 2020
Commodity	Ameren Missouri	Ameren Illinois	Ameren	Ameren Missouri	Ameren Illinois	Ameren
Fuel oils (in gallons)	36	—	36	43	—	43
Natural gas (in mmbtu)	34	114	148	33	114	147
Power (in MWhs)	7	7	14	6	7	13

Derivative Instruments Carrying Value

The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments, as of March 31, 2021, and December 31, 2020:

			March 31, 2021					December 31, 2020
	Balance Sheet Location		Ameren Missouri		Ameren Illinois		Ameren			Ameren Missouri		Ameren Illinois		Ameren
Fuel oils	Other current assets	$	2	$	—	$	2		$	2	$	—	$	2
	Other assets		3		—		3			—		—		—
Natural gas	Other current assets		2		10		12			1		8		9
	Other assets		2		4		6			2		2		4
Power	Other current assets		4		—		4			7		—		7
	Other assets		1		—		1			—		—		—
	Total assets	$	14	$	14	$	28		$	12	$	10	$	22
Fuel oils	Other current liabilities	$	3	$	—	$	3		$	7	$	—	$	7
	Other deferred credits and liabilities		—		—		—			2		—		2
Natural gas	Other current liabilities		—		—		—			1		1		2
	Other deferred credits and liabilities		—		—		—			—		1		1
Power	Other current liabilities		9		16		25			3		17		20
	Other deferred credits and liabilities		5		169		174			8		181		189
	Total liabilities	$	17	$	185	$	202		$	21	$	200	$	221

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Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2021

Fair Value Disclosures [Abstract]

Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis

The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of March 31, 2021, and December 31, 2020:

		March 31, 2021									December 31, 2020
		Level 1		Level 2		Level 3		Total			Level 1		Level 2		Level 3		Total
Assets:
Ameren Missouri
	Derivative assets – commodity contracts:
	Fuel oils	$	4	$	—	$	1	$	5		$	—	$	—	$	2	$	2
	Natural gas	—		4		—		4			—		3		—		3
	Power	2		—		3		5			2		—		5		7
	Total derivative assets – commodity contracts	$	6	$	4	$	4	$	14		$	2	$	3	$	7	$	12
	Nuclear decommissioning trust fund:
	Equity securities:
	U.S. large capitalization	$	679	$	—	$	—	$	679		$	680	$	—	$	—	$	680
	Debt securities:
	U.S. Treasury and agency securities	—		133		—		133			—		115		—		115
	Corporate bonds	—		128		—		128			—		115		—		115
	Other	—		63		—		63			—		67		—		67
	Total nuclear decommissioning trust fund	$	679	$	324	$	—	$	1,003	(a)	$	680	$	297	$	—	$	977	(a)
	Total Ameren Missouri	$	685	$	328	$	4	$	1,017		$	682	$	300	$	7	$	989
Ameren Illinois
	Derivative assets – commodity contracts:
	Natural gas	$	—	$	10	$	4	$	14		$	—	$	6	$	4	$	10
Ameren
	Derivative assets – commodity contracts(b)	$	6	$	14	$	8	$	28		$	2	$	9	$	11	$	22
	Nuclear decommissioning trust fund(c)	679		324		—		1,003		(a)	680		297		—		977		(a)
	Total Ameren	$	685	$	338	$	8	$	1,031		$	682	$	306	$	11	$	999
Liabilities:
Ameren Missouri
	Derivative liabilities – commodity contracts:
	Fuel oils	$	1	$	—	$	2	$	3		$	6	$	—	$	3	$	9
	Natural gas	—		—		—		—			—		1		—		1
	Power	8		—		6		14			8		—		3		11
	Total Ameren Missouri	$	9	$	—	$	8	$	17		$	14	$	1	$	6	$	21
Ameren Illinois
	Derivative liabilities – commodity contracts:
	Natural gas	$	—	$	—	$	—	$	—		$	—	$	1	$	1	$	2
	Power	—		—		185		185			—		—		198		198
	Total Ameren Illinois	$	—	$	—	$	185	$	185		$	—	$	1	$	199	$	200
Ameren
	Derivative liabilities – commodity contracts(b)	$	9	$	—	$	193	$	202		$	14	$	2	$	205	$	221

(a)Balance excludes $7 million and $5 million of cash and cash equivalents, receivables, payables, and accrued income, net, for March 31, 2021, and December 31, 2020, respectively.

(b)See the Ameren Missouri and Ameren Illinois sections of the table for a breakout of the fair value of Ameren’s derivative assets and liabilities by type of commodity.

(c)See the Ameren Missouri section of the table for a breakout of the fair value of Ameren's nuclear decommissioning trust fund by investment type.

Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level Three In The Fair Value Hierarchy

The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the three months ended March 31, 2021 and 2020:

	2021						2020
	Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois		Ameren
For the three months ended March 31:
Beginning balance at January 1	$	2	$	(198)	$	(196)	$	13	$	(224)	$	(211)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities	(5)		9		4		11		(21)		(10)
Settlements	—		4		4		(7)		4		(3)
Ending balance at March 31	$	(3)	$	(185)	$	(188)	$	17	$	(241)	$	(224)
Change in unrealized gains/(losses) related to assets/liabilities held at March 31	$	(3)	$	9	$	6	$	10	$	(21)	$	(11)

Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques

The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of March 31, 2021, and December 31, 2020:

			Fair Value						Weighted Average(b)
	Commodity		Assets		Liabilities	Valuation Technique(s)	Unobservable Input(a)	Range
2021	Power(c)	$	3	$	(191)	Discounted cash flow	Average forward peak and off-peak pricing – forwards/swaps ($/MWh)	23 – 40	29
							Nodal basis ($/MWh)	(5) – 0	(1)
							Trend rate (%)	2 – 5	3
2020	Power(c)	$	5	$	(201)	Discounted cash flow	Average forward peak and off-peak pricing – forwards/swaps ($/MWh)	23 – 37	29
							Nodal basis ($/MWh)	(6) – 0	(2)
							Trend rate (%)	2 – 6	3

(a)Generally, significant increases (decreases) in these inputs in isolation would result in a significantly higher (lower) fair value measurement.

(b)Unobservable inputs were weighted by relative fair value.

(c)Valuations through 2029 use visible forward prices adjusted for nodal-to-hub basis differentials. Valuations beyond 2029 use a trend rate factor and are similarly adjusted for nodal-to-hub basis differentials.

Schedule of Financial Assets and Liabilities

The following table sets forth the carrying amount and, by level within the fair value hierarchy, the fair value of financial assets and liabilities disclosed, but not recorded, at fair value as of March 31, 2021, and December 31, 2020:

	Carrying Amount			Fair Value
				Level 1		Level 2		Level 3			Total
	March 31, 2021
Ameren:
Cash, cash equivalents, and restricted cash	$	172		$	172	$	—	$	—		$	172
Investments in industrial development revenue bonds(a)	256			—		256		—			256
Short-term debt	889			—		889		—			889
Long-term debt (including current portion)(a)	11,535		(b)	—		12,233		507		(c)	12,740
Ameren Missouri:
Cash, cash equivalents, and restricted cash	$	12		$	12	$	—	$	—		$	12
Investments in industrial development revenue bonds(a)	256			—		256		—			256
Short-term debt	204			—		204		—			204
Long-term debt (including current portion)(a)	5,104		(b)	—		5,685		—			5,685
Ameren Illinois:
Cash, cash equivalents, and restricted cash	$	149		$	149	$	—	$	—		$	149
Short-term debt	323			—		323		—			323
Long-term debt (including current portion)	3,947		(b)	—		4,401		—			4,401
	December 31, 2020
Ameren:
Cash, cash equivalents, and restricted cash	$	301		$	301	$	—	$	—		$	301
Investments in industrial development revenue bonds(a)	256			—		256		—			256
Short-term debt	490			—		490		—			490
Long-term debt (including current portion)(a)	11,086		(b)	—		12,778		537		(c)	13,315
Ameren Missouri:
Cash, cash equivalents, and restricted cash	$	145		$	145	$	—	$	—		$	145
Advances to money pool	139			—		139		—			139
Investments in industrial development revenue bonds(a)	256			—		256		—			256
Long-term debt (including current portion)(a)	5,104		(b)	—		6,160		—			6,160
Ameren Illinois:
Cash, cash equivalents, and restricted cash	$	147		$	147	$	—	$	—		$	147
Borrowings from money pool	19			—		19		—			19
Long-term debt (including current portion)	3,946		(b)	—		4,822		—			4,822

(a)Ameren and Ameren Missouri have investments in industrial development revenue bonds, classified as held-to-maturity and recorded in “Other Assets,” that are equal to the finance obligations for the Peno Creek and Audrain CT energy centers. As of March 31, 2021, and December 31, 2020, the carrying amount of both the investments in industrial development revenue bonds and the finance obligations approximated fair value.

(b)Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $86 million, $36 million, and $36 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of March 31, 2021. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $84 million, $36 million, and $36 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2020.

(c)The Level 3 fair value amount consists of ATXI’s senior unsecured notes.

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Related Party Transactions (Tables)

3 Months Ended

Mar. 31, 2021

Related Party Transactions [Abstract]

Schedule of Affiliate Receivables and Payables

The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of March 31, 2021, and December 31, 2020:

	March 31, 2021				December 31, 2020
	Ameren Missouri		Ameren Illinois		Ameren Missouri		Ameren Illinois
Income taxes payable to parent(a)	$	—	$	6	$	—	$	6
Income taxes receivable from parent(b)	14		18		9		15

(a)Included in “Accounts payable – affiliates” on the balance sheet.

(b)Included in “Accounts receivable – affiliates” on the balance sheet.

Schedule of Related Party Transactions

The following table presents the effect on Ameren Missouri and Ameren Illinois of related-party transactions for the three months ended March 31, 2021 and 2020:

				Three Months
Agreement	Income Statement Line Item			Ameren Missouri		Ameren Illinois
Ameren Missouri power supply	Operating Revenues	2021	$	2	$	(a)
agreements with Ameren Illinois		2020		3		(a)
Ameren Missouri and Ameren Illinois	Operating Revenues	2021	$	7	$	(b)
rent and facility services		2020		7		1
Ameren Missouri and Ameren Illinois miscellaneous	Operating Revenues	2021	$	(b)	$	(b)
support services and services provided to ATXI		2020		(b)		(b)
Total Operating Revenues		2021	$	9	$	(b)
		2020		10		1
Ameren Illinois power supply	Purchased Power	2021	$	(a)	$	2
agreements with Ameren Missouri		2020		(a)		3
Ameren Missouri and Ameren Illinois	Purchased Power	2021	$	1	$	(b)
transmission services from ATXI		2020		(a)		(b)
Total Purchased Power		2021	$	1	$	2
		2020		(a)		3
Ameren Missouri and Ameren Illinois	Other Operations and Maintenance	2021	$	(b)	$	1
rent and facility services		2020		(b)		1
Ameren Services support services	Other Operations and Maintenance	2021	$	35	$	33
agreement		2020		35		33
Total Other Operations and		2021	$	35	$	34
Maintenance		2020		35		34
Money pool borrowings (advances)	(Interest Charges)/Other Income, Net	2021	$	(b)	$	(b)
		2020		(b)		(b)

(a)Not applicable.

(b)Amount less than $1 million.

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Callaway Energy Center (Tables)

3 Months Ended

Mar. 31, 2021

Nuclear Waste Matters [Abstract]

Schedule of Insurance Coverage at Callaway Energy Center

The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at April 1, 2021:

Type and Source of Coverage	Most Recent Renewal Date	Maximum Coverages			Maximum Assessments for Single Incidents
Public liability and nuclear worker liability:
American Nuclear Insurers	January 1, 2021	$	450		$	—
Pool participation	(a)	13,210		(a)	138		(b)
		$	13,660	(c)	$	138
Property damage:
NEIL and EMANI	April 1, 2021	$	3,200	(d)	$	25	(e)
Replacement power:
NEIL	April 1, 2021	$	490	(f)	$	7	(e)

(a)Provided through mandatory participation in an industrywide retrospective premium assessment program. The maximum coverage available is dependent on the number of United States commercial reactors participating in the program.

(b)Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $450 million in the event of an incident at any licensed United States commercial reactor, payable at $21 million per year.

(c)Limit of liability for each incident under the Price-Anderson liability provisions of the Atomic Energy Act of 1954, as amended. This limit is subject to change to account for the effects of inflation and changes in the number of licensed power reactors.

(d)NEIL provides $2.7 billion in property damage, stabilization, decontamination, and premature decommissioning insurance for radiation events and $2.3 billion in property damage insurance for nonradiation events. EMANI provides $490 million in property damage insurance for both radiation and nonradiation events.

(e)All NEIL-insured plants could be subject to assessments should losses exceed the accumulated funds from NEIL.

(f)Provides replacement power cost insurance in the event of a prolonged accidental outage. Weekly indemnity up to $4.5 million for 52 weeks, which commences after the first 12 weeks of an outage, plus up to $3.6 million per week for a minimum of 71 weeks thereafter for a total not exceeding the policy limit of $490 million. Nonradiation events are limited to $328 million.

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Retirement Benefits (Tables)

3 Months Ended

Mar. 31, 2021

Retirement Benefits [Abstract]

Components Of Net Periodic Benefit Cost

The following table presents the components of the net periodic benefit cost (income) incurred for Ameren’s pension and postretirement benefit plans for the three months ended March 31, 2021 and 2020:

	Pension Benefits				Postretirement Benefits
	Three Months				Three Months
	2021		2020		2021		2020
Service cost(a)	$	33	$	27	$	6	$	4
Non-service cost components:
Interest cost	38		43		8		10
Expected return on plan assets	(75)		(73)		(20)		(20)
Amortization of:
Prior service benefit	—		—		(1)		(1)
Actuarial loss (gain)	17		14		(1)		(2)
Total non-service cost components(b)	$	(20)	$	(16)	$	(14)	$	(13)
Net periodic benefit cost (income)	$	13	$	11	$	(8)	$	(9)

(a)Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income.

(b)Non-service cost components are reflected in “Other Income, Net” on Ameren’s statement of income. See Note 5 – Other Income, Net, for additional information.

Summary Of Benefit Plan Costs Incurred

Ameren Missouri and Ameren Illinois are responsible for their respective share of Ameren’s pension and other postretirement costs. The following table presents the respective share of net periodic pension and other postretirement benefit costs (income) incurred for the three months ended March 31, 2021 and 2020:

	Pension Benefits				Postretirement Benefits
	Three Months				Three Months
	2021		2020		2021		2020
Ameren Missouri(a)	$	6	$	4	$	(1)	$	(1)
Ameren Illinois	8		7		(7)		(8)
Other	(1)		—		—		—
Ameren(a)	$	13	$	11	$	(8)	$	(9)

(a)Does not include the impact of the regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates.

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Income Taxes Income Taxes (Tables)

3 Months Ended

Mar. 31, 2021

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

The following table presents a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the three months ended March 31, 2021 and 2020:

	Ameren		Ameren Missouri		Ameren Illinois
	2021	2020	2021	2020	2021	2020
Three Months
Federal statutory corporate income tax rate:	21%	21%	21%	21%	21%	21%
Increases (decreases) from:
Amortization of deferred investment tax credit	(1)	—	(1)	(1)	—	—
Amortization of excess deferred taxes	(9)	(9)	(17)	(15)	(2)	(3)
Depreciation differences	—	(1)	1	—	(1)	(1)
Renewable and other tax credits	(6)	—	(11)	—	—	—
State tax	6	6	3	3	7	7
Stock-based compensation	(1)	(5)	—	—	—	—
Effective income tax rate	10%	12%	(4)%	8%	25%	24%

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Supplemental Information (Tables)

3 Months Ended

Mar. 31, 2021

Supplemental Information [Abstract]

Schedule of Cash and Cash Equivalents Including Restricted Cash

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows as of March 31, 2021, and December 31, 2020:

	March 31, 2021						December 31, 2020
	Ameren		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois
Cash and cash equivalents	$	6	$	1	$	—	$	139	$	136	$	—
Restricted cash	134		—		125		17		—		6
Restricted cash included in “Other current assets”	—		3		—		—		5		—
Restricted cash included in “Other assets”	24		—		24		141		—		141
Restricted cash included in “Nuclear decommissioning trust fund”	8		8		—		4		4		—
Total cash, cash equivalents, and restricted cash	$	172	$	12	$	149	$	301	$	145	$	147

Schedule of Accounts, Notes, Loans and Financing Receivable

The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the three months ended March 31, 2021 and 2020:

	Three Months
	2021		2020
Ameren:
Beginning of period	$	50	$	17
Bad debt expense	4		3
Net write-offs	(7)		(1)
End of period	$	47	$	19
Ameren Missouri:
Beginning of period	$	16	$	7
Bad debt expense	1		2
Net write-offs	(2)		(1)
End of period	$	15	$	8
Ameren Illinois:(a)
Beginning of Period	$	34	$	10
Bad debt expense	3		1
Net write-offs	(5)		—
End of Period	$	32	$	11

(a)Ameren Illinois has rate-adjustment mechanisms that allow it to recover the difference between its actual net bad debt write-offs under GAAP, including those associated with receivables purchased from alternative retail electric suppliers, and the amount of net bad debt write-offs included in its base rates.

Schedule of Cash Flow, Supplemental Disclosures

Supplemental Cash Flow Information

The following table provides noncash financing and investing activity excluded from the statements of cash flows for the three months ended March 31, 2021 and 2020:

	March 31, 2021						March 31, 2020
	Ameren		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois
Investing
Accrued capital expenditures, including wind generation expenditures	$	271	$	141	$	139	$	235	$	97	$	127
Accrued nuclear fuel expenditures	—		—		—		7		7		—
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund	22		22		—		(111)		(111)		—
Financing
Issuance of common stock for stock-based compensation	33		—		—		38		—		—

Asset Retirement Obligation Disclosure

The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the three months ended March 31, 2021:

	Ameren Missouri			Ameren Illinois			Ameren
Balance at December 31, 2020	$	751		$	5	(a)	$	756	(b)
Liabilities incurred (c)	10			—			10
Liabilities settled	(3)			—			(3)
Accretion	8		(d)	—			8		(d)
Change in estimates	(7)		(e)	—			(7)		(e)
Balance at March 31, 2021	$	759		$	5	(a)	$	764	(b)

(a)Included in “Other deferred credits and liabilities” on the balance sheet.

(b)Balance included $59 million and $60 million in “Other current liabilities” on the balance sheet as of March 31, 2021, and December 31, 2020, respectively.

(c)In the first quarter of 2021, Ameren Missouri recorded an ARO related to the decommissioning for the Atchison Renewable Energy Center.

(d)Accretion expense attributable to Ameren Missouri was recorded as a decrease to regulatory liabilities.

(e)Ameren Missouri changed its fair value estimate primarily due to a decrease in the cost estimate for closure of certain CCR storage facilities.

Schedule of excise taxes

The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the three months ended March 31, 2021 and 2020:

	Three Months
	2021		2020
Ameren Missouri	$	31	$	30
Ameren Illinois	39		35
Ameren	$	70	$	65

Schedule of Earnings Per Share, Basic and Diluted

The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three months ended March 31, 2021 and 2020:

	Three Months
	2021	2020
Weighted-average Common Shares Outstanding – Basic	254.4	246.4
Assumed settlement of performance share units and restricted stock units	1.5	1.1
Dilutive effect of forward sale agreement	—	0.6
Weighted-average Common Shares Outstanding – Diluted(a)	255.9	248.1

(a)There were no potentially dilutive securities excluded from the earnings per diluted share calculations for the three months ended March 31, 2021 and 2020.

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Segment Information (Tables)

3 Months Ended

Mar. 31, 2021

Segment Reporting [Abstract]

Schedule Of Segment Reporting Information By Segment

The following tables present revenues, net income (loss) attributable to common shareholders, and capital expenditures by segment at Ameren and Ameren Illinois for the three months ended March 31, 2021 and 2020. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount. For additional information about our segments, see Note 16 – Segment Information under Part II, Item 8, of the Form 10-K.

Ameren

	Ameren Missouri			Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission			Other		Intersegment Eliminations		Ameren
Three Months 2021:
External revenues	$	695		$	411	$	347	$	113		$	—	$	—	$	1,566
Intersegment revenues	9			—		—		17			—		(26)		—
Net income attributable to Ameren common shareholders	47			46		75		47		(a)	18		—		233
Capital expenditures	534		(b)	157		48		141			1		6		887		(b)
Three Months 2020:
External revenues	$	670		$	389	$	271	$	110		$	—	$	—	$	1,440
Intersegment revenues	10			1		—		13			—		(24)		—
Net income (loss) attributable to Ameren common shareholders	(10)			37		55		47		(a)	17		—		146
Capital expenditures	278			123		61		170			3		1		636

(a)Ameren Transmission earnings reflect an allocation of financing costs from Ameren (parent).

(b)Includes $193 million at Ameren and Ameren Missouri for wind generation expenditures for the three months ended March 31, 2021.

Ameren Illinois

	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Intersegment Eliminations		Ameren Illinois
Three Months 2021:
External revenues	$	411	$	347	$	65	$	—	$	823
Intersegment revenues	—		—		16		(16)		—
Net income available to common shareholder	46		75		28		—		149
Capital expenditures	157		48		132		—		337
Three Months 2020:
External revenues	$	390	$	271	$	62	$	—	$	723
Intersegment revenues	—		—		12		(12)		—
Net income available to common shareholder	37		55		28		—		120
Capital expenditures	123		61		140		—		324

Disaggregation of Revenue

The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three months ended March 31, 2021 and 2020. Economic factors affect the nature, timing, amount, and uncertainty of revenues and cash flows in a similar manner across customer classes. Revenues from alternative revenue programs have a similar distribution among customer classes as revenues from contracts with customers. Other revenues not associated with contracts with customers are presented in the Other customer classification, along with electric transmission and off-system revenues.

Ameren

	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Intersegment Eliminations		Ameren
Three Months 2021:
Residential	$	312	$	229	$	—	$	—	$	—	$	541
Commercial	216		132		—		—		—		348
Industrial	52		34		—		—		—		86
Other	61		16		—		130		(26)		181
Total electric revenues	$	641	$	411	$	—	$	130	$	(26)	$	1,156
Residential	$	34	$	—	$	251	$	—	$	—	$	285
Commercial	15		—		64		—		—		79
Industrial	1		—		14		—		—		15
Other	13		—		18		—		—		31
Total natural gas revenues	$	63	$	—	$	347	$	—	$	—	$	410
Total revenues(a)	$	704	$	411	$	347	$	130	$	(26)	$	1,566
Three Months 2020:
Residential	$	297	$	220	$	—	$	—	$	—	$	517
Commercial	221		126		—		—		—		347
Industrial	53		35		—		—		—		88
Other	60		9		—		123		(24)		168
Total electric revenues	$	631	$	390	$	—	$	123	$	(24)	$	1,120
Residential	$	33	$	—	$	213	$	—	$	—	$	246
Commercial	13		—		54		—		—		67
Industrial	1		—		3		—		—		4
Other	2		—		1		—		—		3
Total natural gas revenues	$	49	$	—	$	271	$	—	$	—	$	320
Total revenues(a)	$	680	$	390	$	271	$	123	$	(24)	$	1,440

(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three months ended March 31, 2021 and 2020:

	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Ameren
Three Months 2021:
Revenues from alternative revenue programs	$	(10)	$	61	$	3	$	(1)	$	53
Other revenues not from contracts with customers	(2)		3		1		—		2
Three Months 2020:
Revenues from alternative revenue programs	$	(3)	$	46	$	11	$	12	$	66
Other revenues not from contracts with customers	8		1		1		—		10

Ameren Illinois

	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Intersegment Eliminations		Ameren Illinois
Three Months 2021:
Residential	$	229	$	251	$	—	$	—	$	480
Commercial	132		64		—		—		196
Industrial	34		14		—		—		48
Other	16		18		81		(16)		99
Total revenues(a)	$	411	$	347	$	81	$	(16)	$	823
Three Months 2020:
Residential	$	220	$	213	$	—	$	—	$	433
Commercial	126		54		—		—		180
Industrial	35		3		—		—		38
Other	9		1		74		(12)		72
Total revenues(a)	$	390	$	271	$	74	$	(12)	$	723

(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three months ended March 31, 2021 and 2020:

	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Ameren Illinois
Three Months 2021:
Revenues from alternative revenue programs	$	61	$	3	$	(1)	$	63
Other revenues not from contracts with customers	3		1		—		4
Three Months 2020:
Revenues from alternative revenue programs	$	46	$	11	$	10	$	67
Other revenues not from contracts with customers	1		1		—		2

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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Basis Of Presentation And Significant Accounting Policies [Line Items]
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	27.00%		21.00%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 137		$ 99
Noncontrolling Interest in Variable Interest Entity	41	$ 37
Cash Surrender Value of Life Insurance	275	272
Corporate owned life insurance, borrowings	$ 107	107
Union Electric Company
Basis Of Presentation And Significant Accounting Policies [Line Items]
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	19.00%		16.00%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 33		$ 29
Union Electric Company | Final Rate Order
Basis Of Presentation And Significant Accounting Policies [Line Items]
COVID-19 pandemic costs	$ 9
Ameren Illinois Company
Basis Of Presentation And Significant Accounting Policies [Line Items]
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	32.00%		25.00%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 104		$ 70
Cash Surrender Value of Life Insurance	117	115
Corporate owned life insurance, borrowings	107	$ 107
Partnership Funding Commitment
Basis Of Presentation And Significant Accounting Policies [Line Items]
Unrecorded Unconditional Purchase Obligation	$ 33

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Rate And Regulatory Matters (Narrative-Missouri) (Detail) $ in Millions	1 Months Ended	3 Months Ended
	Jan. 31, 2021 MWh	Mar. 31, 2021 USD ($) MWh	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
Rate And Regulatory Matters [Line Items]
Regulatory assets		$ 1,249		$ 1,100
Revenues		1,566	$ 1,440
Union Electric Company
Rate And Regulatory Matters [Line Items]
Regulatory assets		413		$ 347
Pending Rate Case | Electricity | Union Electric Company
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 299
Public Utilities, Requested Return on Equity, Percentage		9.90%
Public Utilities, Requested Equity Capital Structure, Percentage		51.90%
Rate Base		$ 10,000
Months to complete a rate proceeding		11 months
Pending Rate Case | Natural Gas | Union Electric Company
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 9
Public Utilities, Requested Return on Equity, Percentage		9.80%
Public Utilities, Requested Equity Capital Structure, Percentage		51.90%
Rate Base		$ 310
Months to complete a rate proceeding		11 months
Wind Generation Facility | Union Electric Company
Rate And Regulatory Matters [Line Items]
Amount of Megawatts | MWh	300	700
Atchison Renewable Energy Center purchase price		$ 250
Final Rate Order | Union Electric Company
Rate And Regulatory Matters [Line Items]
COVID-19 pandemic costs		9
Regulatory assets		5
Revenues		$ 4

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Rate And Regulatory Matters (Narrative-Illinois) (Detail) - Ameren Illinois Company - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2021	Mar. 31, 2021
Rate And Regulatory Matters [Line Items]
Annual investment in energy-efficiency programs		$ 100
Deferred payment arrangement extension		18 months
Financial assistance program costs		$ 4
IEIMA
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Return on Equity, Percentage		5.80%
Final Rate Order | IEIMA | Electric Distribution
Rate And Regulatory Matters [Line Items]
Requested electric distribution service rate reconciliation period		2 years
Amortization Period		two years
Subsequent Event | Pending Rate Case | IEIMA | Electric Distribution
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 64

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Rate And Regulatory Matters (Narrative-Federal) (Detail) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	May 31, 2020	Nov. 30, 2019	Mar. 31, 2021	Dec. 31, 2020
Rate And Regulatory Matters [Line Items]
Regulatory liabilities			$ 5,230	$ 5,282
Current regulatory liabilities			225	121
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Regulatory liabilities			1,988	2,063
Current regulatory liabilities			200	$ 88
Final Rate Order | Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Regulatory liabilities			$ 9
Midwest Independent Transmission System Operator, Inc
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Return on Equity, Percentage			12.38%
Midwest Independent Transmission System Operator, Inc | Final Rate Order
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Return on Equity, Percentage	10.02%	9.88%	10.32%
Customer Requested Rate on Equity			9.15%
Incentive adder to FERC allowed base return on common equity			0.50%
Current regulatory liabilities			$ 17
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Current regulatory liabilities			$ 9
Maximum | Midwest Independent Transmission System Operator, Inc | Final Rate Order
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Return on Equity, Percentage			10.82%

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Short-Term Debt And Liquidity (Narrative) (Details) $ in Billions	3 Months Ended
	Mar. 31, 2021 USD ($)	Mar. 31, 2020
Credit Agreements
Short-term Debt [Line Items]
Net Liquidity Available	$ 1.4
Actual debt-to-capital ratio	0.57
Utilities
Short-term Debt [Line Items]
Short-term Debt, Weighted Average Interest Rate, over Time	0.22%	1.93%
Union Electric Company | Missouri Credit Agreement
Short-term Debt [Line Items]
Actual debt-to-capital ratio	0.49
Ameren Illinois Company | Illinois Credit Agreement
Short-term Debt [Line Items]
Actual debt-to-capital ratio	0.46

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Short-Term Debt and Liquidity (Short-Term Debt outstanding) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Short-term Debt [Line Items]
Short-term debt	$ 889	$ 490
Union Electric Company
Short-term Debt [Line Items]
Short-term debt	204	0
Ameren Illinois Company
Short-term Debt [Line Items]
Short-term debt	323	0
Commercial Paper
Short-term Debt [Line Items]
Short-term debt	889	490
Commercial Paper | Ameren (parent)
Short-term Debt [Line Items]
Short-term debt	362	490
Commercial Paper | Union Electric Company
Short-term Debt [Line Items]
Short-term debt	204	0
Commercial Paper | Ameren Illinois Company
Short-term Debt [Line Items]
Short-term debt	$ 323	$ 0

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Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Short-term Debt [Line Items]
Short-term Debt, Average Outstanding Amount	$ 649	$ 628
Weighted-average interest rate	0.24%	1.89%
Short-term Debt, Maximum Amount Outstanding During Period	$ 916	$ 908
Peak interest rate	0.33%	5.05%
Ameren (parent)
Short-term Debt [Line Items]
Short-term Debt, Average Outstanding Amount	$ 454	$ 157
Weighted-average interest rate	0.25%	1.94%
Short-term Debt, Maximum Amount Outstanding During Period	$ 650	$ 425
Peak interest rate	0.33%	3.30%
Union Electric Company
Short-term Debt [Line Items]
Short-term Debt, Average Outstanding Amount	$ 99	$ 395
Weighted-average interest rate	0.22%	1.86%
Short-term Debt, Maximum Amount Outstanding During Period	$ 206	$ 573
Peak interest rate	0.25%	5.05%
Ameren Illinois Company
Short-term Debt [Line Items]
Short-term Debt, Average Outstanding Amount	$ 96	$ 76
Weighted-average interest rate	0.21%	1.99%
Short-term Debt, Maximum Amount Outstanding During Period	$ 353	$ 150
Peak interest rate	0.25%	3.40%

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Long-Term debt and Equity Financings (Narrative) (Details) - USD ($) shares in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Feb. 11, 2021
Long-Term Debt And Equity Financings [Line Items]
Stock Issued During Period, Shares, New Issues	0.1	0.2
Issuance of common stock	$ 125,000,000	$ 13,000,000
Stock Issued During Period, Shares, Other	0.5	0.5
Issuance of common stock for stock-based compensation	$ 33,000,000	$ 38,000,000
Shares issued under forward sale agreement (in shares)	1.6	0.0	1.6
Common Stock Value Issued Through Forward Sale Agreement			$ 113,000,000
Dividend reinvestment and 401 (k) plans
Long-Term Debt And Equity Financings [Line Items]
Issuance of common stock	$ 12,000,000
Ameren (parent) | Unsecured Debt | Senior Secured Notes 1.75% Due 2028 [Domain]
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 450,000,000
Debt Instrument, Interest Rate, Stated Percentage	1.75%
Proceeds from Issuance of Debt	$ 447,000,000
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Issuance of common stock for stock-based compensation	0	$ 0
Capital contributions from parent	113,000,000	0
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Issuance of common stock for stock-based compensation	0	0
Capital contributions from parent	40,000,000	100,000,000
Redemption of preferred stock	$ (13,000,000)	$ 0
Ameren Illinois Company | Series6625
Long-Term Debt And Equity Financings [Line Items]
Preferred Stock, Dividend Rate, Percentage	6.625%
Redemption of preferred stock	$ (12,000,000)
Ameren Illinois Company | Series775
Long-Term Debt And Equity Financings [Line Items]
Preferred Stock, Dividend Rate, Percentage	7.75%
Redemption of preferred stock	$ (1,000,000)

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Other Income, Net (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	$ 7	$ 4
Interest income on industrial development revenue bonds	6	6
Other interest income	1	1
Non-service cost components of net periodic benefit income	34	23
Miscellaneous income	4	2
Donations	(3)	(13)
Miscellaneous expense	(3)	(2)
Total Other Income, Net	46	21
Union Electric Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	4	2
Interest income on industrial development revenue bonds	6	6
Non-service cost components of net periodic benefit income	14	5
Miscellaneous income	1	1
Donations	0	(8)
Miscellaneous expense	(2)	(2)
Total Other Income, Net	23	4
Defined Benefit Plan, Non-service Cost or Income Components - Tracker	(1)	6
Ameren Illinois Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	3	2
Other interest income	1	1
Non-service cost components of net periodic benefit income	14	13
Miscellaneous income	0	1
Donations	(3)	(4)
Miscellaneous expense	(1)	(2)
Total Other Income, Net	$ 14	11
Final Rate Order | Electricity | Union Electric Company
Other Nonoperating Income (Expense) [Line Items]
Donations		$ (8)

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Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Detail) gal in Millions, MWh in Millions, MMBTU in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021 MMBTU MWh gal	Dec. 31, 2020 MWh MMBTU gal
Fuel Oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	36	43
Natural Gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	148	147
Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	14	13
Union Electric Company | Fuel Oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	36	43
Union Electric Company | Natural Gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	34	33
Union Electric Company | Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	7	6
Ameren Illinois Company | Fuel Oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	0	0
Ameren Illinois Company | Natural Gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	114	114
Ameren Illinois Company | Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	7	7

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Derivative Financial Instruments (Derivative Instruments Carrying Value) (Detail) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Derivative assets	$ 28	$ 22
Derivative liabilities	202	221
Fuel Oils | Other Current Assets
Derivative [Line Items]
Derivative assets	2	2
Fuel Oils | Other Assets
Derivative [Line Items]
Derivative assets	3	0
Fuel Oils | Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	3	7
Fuel Oils | Other Deferred Credits And Liabilities
Derivative [Line Items]
Derivative liabilities	0	2
Natural Gas | Other Current Assets
Derivative [Line Items]
Derivative assets	12	9
Natural Gas | Other Assets
Derivative [Line Items]
Derivative assets	6	4
Natural Gas | Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	0	2
Natural Gas | Other Deferred Credits And Liabilities
Derivative [Line Items]
Derivative liabilities	0	1
Power | Other Current Assets
Derivative [Line Items]
Derivative assets	4	7
Power | Other Assets
Derivative [Line Items]
Derivative assets	1	0
Power | Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	25	20
Power | Other Deferred Credits And Liabilities
Derivative [Line Items]
Derivative liabilities	174	189
Union Electric Company
Derivative [Line Items]
Derivative assets	14	12
Derivative liabilities	17	21
Union Electric Company | Fuel Oils | Other Current Assets
Derivative [Line Items]
Derivative assets	2	2
Union Electric Company | Fuel Oils | Other Assets
Derivative [Line Items]
Derivative assets	3	0
Union Electric Company | Fuel Oils | Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	3	7
Union Electric Company | Fuel Oils | Other Deferred Credits And Liabilities
Derivative [Line Items]
Derivative liabilities	0	2
Union Electric Company | Natural Gas | Other Current Assets
Derivative [Line Items]
Derivative assets	2	1
Union Electric Company | Natural Gas | Other Assets
Derivative [Line Items]
Derivative assets	2	2
Union Electric Company | Natural Gas | Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	0	1
Union Electric Company | Natural Gas | Other Deferred Credits And Liabilities
Derivative [Line Items]
Derivative liabilities	0	0
Union Electric Company | Power | Other Current Assets
Derivative [Line Items]
Derivative assets	4	7
Union Electric Company | Power | Other Assets
Derivative [Line Items]
Derivative assets	1	0
Union Electric Company | Power | Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	9	3
Union Electric Company | Power | Other Deferred Credits And Liabilities
Derivative [Line Items]
Derivative liabilities	5	8
Ameren Illinois Company
Derivative [Line Items]
Derivative assets	14	10
Derivative liabilities	185	200
Ameren Illinois Company | Fuel Oils | Other Current Assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company | Fuel Oils | Other Assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company | Fuel Oils | Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	0	0
Ameren Illinois Company | Fuel Oils | Other Deferred Credits And Liabilities
Derivative [Line Items]
Derivative liabilities	0	0
Ameren Illinois Company | Natural Gas | Other Current Assets
Derivative [Line Items]
Derivative assets	10	8
Ameren Illinois Company | Natural Gas | Other Assets
Derivative [Line Items]
Derivative assets	4	2
Ameren Illinois Company | Natural Gas | Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	0	1
Ameren Illinois Company | Natural Gas | Other Deferred Credits And Liabilities
Derivative [Line Items]
Derivative liabilities	0	1
Ameren Illinois Company | Power | Other Current Assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company | Power | Other Assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company | Power | Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	16	17
Ameren Illinois Company | Power | Other Deferred Credits And Liabilities
Derivative [Line Items]
Derivative liabilities	$ 169	$ 181

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Fair Value Measurements (Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	$ 1,003	$ 977
Assets fair value	1,031	999
Excluded receivables, payables, and accrued income, net	7	5
Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	679	680
Assets fair value	685	682
Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	324	297
Assets fair value	338	306
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Assets fair value	8	11
Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	28	22
Derivative liabilities	202	221
Commodity Contract | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	6	2
Derivative liabilities	9	14
Commodity Contract | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	14	9
Derivative liabilities	0	2
Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	8	11
Derivative liabilities	193	205
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	1,003	977
Assets fair value	1,017	989
Union Electric Company | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	679	680
Assets fair value	685	682
Union Electric Company | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	324	297
Assets fair value	328	300
Union Electric Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Assets fair value	4	7
Union Electric Company | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	14	12
Derivative liabilities	17	21
Union Electric Company | Commodity Contract | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	6	2
Derivative liabilities	9	14
Union Electric Company | Commodity Contract | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	4	3
Derivative liabilities	0	1
Union Electric Company | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	4	7
Derivative liabilities	8	6
Union Electric Company | Fuel Oils | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	5	2
Derivative liabilities	3	9
Union Electric Company | Fuel Oils | Commodity Contract | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	4	0
Derivative liabilities	1	6
Union Electric Company | Fuel Oils | Commodity Contract | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Union Electric Company | Fuel Oils | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	1	2
Derivative liabilities	2	3
Union Electric Company | Natural Gas | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	4	3
Derivative liabilities	0	1
Union Electric Company | Natural Gas | Commodity Contract | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Union Electric Company | Natural Gas | Commodity Contract | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	4	3
Derivative liabilities	0	1
Union Electric Company | Natural Gas | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Union Electric Company | Power | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	5	7
Derivative liabilities	14	11
Union Electric Company | Power | Commodity Contract | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	2	2
Derivative liabilities	8	8
Union Electric Company | Power | Commodity Contract | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Union Electric Company | Power | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	3	5
Derivative liabilities	6	3
Union Electric Company | Equity Securities | U.S. large capitalization
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	679	680
Union Electric Company | Equity Securities | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1) | U.S. large capitalization
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	679	680
Union Electric Company | Equity Securities | Significant Other Observable Inputs (Level 2) | U.S. large capitalization
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Equity Securities | Level 3 | U.S. large capitalization
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Debt Securities | US treasury and government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	133	115
Union Electric Company | Debt Securities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	128	115
Union Electric Company | Debt Securities | Other Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	63	67
Union Electric Company | Debt Securities | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1) | US treasury and government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Debt Securities | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1) | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Debt Securities | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1) | Other Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Debt Securities | Significant Other Observable Inputs (Level 2) | US treasury and government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	133	115
Union Electric Company | Debt Securities | Significant Other Observable Inputs (Level 2) | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	128	115
Union Electric Company | Debt Securities | Significant Other Observable Inputs (Level 2) | Other Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	63	67
Union Electric Company | Debt Securities | Level 3 | US treasury and government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Debt Securities | Level 3 | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Debt Securities | Level 3 | Other Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Ameren Illinois Company | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	185	200
Ameren Illinois Company | Commodity Contract | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	0	0
Ameren Illinois Company | Commodity Contract | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	0	1
Ameren Illinois Company | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	185	199
Ameren Illinois Company | Natural Gas | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	14	10
Derivative liabilities	0	2
Ameren Illinois Company | Natural Gas | Commodity Contract | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Ameren Illinois Company | Natural Gas | Commodity Contract | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	10	6
Derivative liabilities	0	1
Ameren Illinois Company | Natural Gas | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	4	4
Derivative liabilities	0	1
Ameren Illinois Company | Power | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	185	198
Ameren Illinois Company | Power | Commodity Contract | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	0	0
Ameren Illinois Company | Power | Commodity Contract | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	0	0
Ameren Illinois Company | Power | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	$ 185	$ 198

XML

Fair Value Measurements (Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level Three In The Fair Value Hierarchy) (Detail) - Power - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	$ (188)	$ (224)	$ (196)	$ (211)
Included in regulatory assets/liabilities	4	(10)
Settlements, assets	4
Settlement, liabilities		(3)
Change in unrealized gains (losses) related to assets/liabilities held at period end	6	(11)
Union Electric Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	(3)	17	2	13
Included in regulatory assets/liabilities	(5)	11
Settlement, liabilities	0	(7)
Change in unrealized gains (losses) related to assets/liabilities held at period end	(3)	10
Ameren Illinois Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	(185)	(241)	$ (198)	$ (224)
Included in regulatory assets/liabilities	9	(21)
Settlements, assets	4	4
Change in unrealized gains (losses) related to assets/liabilities held at period end	$ 9	$ (21)

XML

Fair Value Measurements (Schedule Of Valuation Process And Unobservable Inputs) (Detail) - Power $ in Millions	Mar. 31, 2021 USD ($) $ / MWh $ / MMBTU	Dec. 31, 2020 USD ($) $ / MWh $ / MMBTU
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivative assets | $	$ 3	$ 5
Derivative liabilities | $	$ (191)	$ (201)
Commodity Forward Price | Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	23	23
Commodity Forward Price | Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	40	37
Commodity Forward Price | Discounted Cash Flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	29	29
Nodal Basis | Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	(5)	(6)
Nodal Basis | Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	0	0
Nodal Basis | Discounted Cash Flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	(1)	(2)
Commodity Future Price | Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input | $ / MMBTU	2	2
Commodity Future Price | Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input | $ / MMBTU	5	6
Commodity Future Price | Discounted Cash Flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input | $ / MMBTU	3	3

XML

Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 172	$ 301	$ 203	$ 176
Short-term debt	889	490
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	12	145	24	39
Advances to money pool	0	139
Short-term debt	204	0
Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	149	147	$ 140	$ 125
Short-term debt	323	0
Borrowings from money pool	0	19
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	172	301
Available-for-sale Securities and Held-to-maturity Securities	256	256
Short-term debt	889	490
Long-term debt (including current portion)	11,535	11,086
Debt Issuance Costs, Net	86	84
Carrying Amount | Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	12	145
Advances to money pool		139
Available-for-sale Securities and Held-to-maturity Securities	256	256
Short-term debt	204
Long-term debt (including current portion)	5,104	5,104
Debt Issuance Costs, Net	36	36
Carrying Amount | Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	149	147
Short-term debt	323
Long-term debt (including current portion)	3,947	3,946
Debt Issuance Costs, Net	36	36
Borrowings from money pool		19
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	172	301
Investments, Fair Value Disclosure	256	256
Short-term Debt, Fair Value	889	490
Long-term Debt, Fair Value	12,740	13,315
Fair Value | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	172	301
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0
Investments, Fair Value Disclosure	256	256
Short-term Debt, Fair Value	889	490
Long-term Debt, Fair Value	12,233	12,778
Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	507	537
Fair Value | Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	12	145
Advances to money pool		139
Investments, Fair Value Disclosure	256	256
Short-term Debt, Fair Value	204
Long-term Debt, Fair Value	5,685	6,160
Fair Value | Union Electric Company | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	12	145
Advances to money pool		0
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0
Long-term Debt, Fair Value	0	0
Fair Value | Union Electric Company | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0
Advances to money pool		139
Investments, Fair Value Disclosure	256	256
Short-term Debt, Fair Value	204
Long-term Debt, Fair Value	5,685	6,160
Fair Value | Union Electric Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0
Advances to money pool		0
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0
Long-term Debt, Fair Value	0	0
Fair Value | Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	149	147
Short-term Debt, Fair Value	323
Long-term Debt, Fair Value	4,401	4,822
Borrowings from money pool		19
Fair Value | Ameren Illinois Company | Quoted Prices In Active Markets For Identical Assets or Liabilities (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	149	147
Short-term Debt, Fair Value	0
Long-term Debt, Fair Value	0	0
Borrowings from money pool		0
Fair Value | Ameren Illinois Company | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0
Short-term Debt, Fair Value	323
Long-term Debt, Fair Value	4,401	4,822
Borrowings from money pool		19
Fair Value | Ameren Illinois Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0	0
Short-term Debt, Fair Value	0
Long-term Debt, Fair Value	$ 0	0
Borrowings from money pool		$ 0

XML

Related Party Transactions (Narrative) (Details) - Ameren Illinois Company - April 2021 Procurement - Ameren Illinois Power Supply Agreements with Ameren Missouri	3 Months Ended
	Mar. 31, 2021 MWh $ / MWh
Related Party Transaction [Line Items]
Related Party Long Term Contract For Purchase of Electric Power | MWh	33,600
Related Party Long Term Contract For Purchase of Electric Power Rate | $ / MWh	34

XML

Related Party Transactions (Schedule of Affiliate Receivables and Payables) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Union Electric Company
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	$ 40	$ 46
Accounts Receivable, Related Parties, Current	69	57
Union Electric Company | Income taxes payable to parent
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	0	0
Union Electric Company | Income taxes receivable from parent
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	14	9
Ameren Illinois Company
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	43	51
Accounts Receivable, Related Parties, Current	71	64
Ameren Illinois Company | Income taxes payable to parent
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	6	6
Ameren Illinois Company | Income taxes receivable from parent
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	$ 18	$ 15

XML

Related Party Transactions (Effects of Related-party Transactions on the Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Union Electric Company | Ameren Missouri Power Supply Agreements with Ameren Illinois
Related Party Transaction [Line Items]
Operating Revenues	$ 2	$ 3
Union Electric Company | Ameren Missouri and Ameren Illinois Rent and Facility Services
Related Party Transaction [Line Items]
Operating Revenues	7	7
Operating Expenses	1	1
Union Electric Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services
Related Party Transaction [Line Items]
Operating Revenues	1	1
Union Electric Company | Total Related Party Operating Revenues
Related Party Transaction [Line Items]
Operating Revenues	9	10
Union Electric Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI
Related Party Transaction [Line Items]
Operating Expenses	1
Union Electric Company | Purchased Power
Related Party Transaction [Line Items]
Operating Expenses	1
Union Electric Company | Ameren Services Support Services Agreement
Related Party Transaction [Line Items]
Operating Expenses	35	35
Union Electric Company | Total Related Party Other Operations and Maintenance
Related Party Transaction [Line Items]
Operating Expenses	35	35
Union Electric Company | Money pool borrowings (advances)
Related Party Transaction [Line Items]
Interest Charges (Income)	1	1
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Rent and Facility Services
Related Party Transaction [Line Items]
Operating Revenues	1	1
Operating Expenses	1	1
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services
Related Party Transaction [Line Items]
Operating Revenues	1	1
Ameren Illinois Company | Total Related Party Operating Revenues
Related Party Transaction [Line Items]
Operating Revenues	1	1
Ameren Illinois Company | Ameren Illinois Power Supply Agreements with Ameren Missouri
Related Party Transaction [Line Items]
Operating Expenses	2	3
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI
Related Party Transaction [Line Items]
Operating Expenses	1	1
Ameren Illinois Company | Purchased Power
Related Party Transaction [Line Items]
Operating Expenses	2	3
Ameren Illinois Company | Ameren Services Support Services Agreement
Related Party Transaction [Line Items]
Operating Expenses	33	33
Ameren Illinois Company | Total Related Party Other Operations and Maintenance
Related Party Transaction [Line Items]
Operating Expenses	34	34
Ameren Illinois Company | Money pool borrowings (advances)
Related Party Transaction [Line Items]
Interest Charges (Income)	$ 1	$ 1

XML

Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions	Mar. 31, 2021 USD ($) center scrubber site	Dec. 31, 2020 USD ($)
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 764	$ 756
Minimum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	175
Maximum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	$ 225
Union Electric Company
Loss Contingencies [Line Items]
Number of Energy Center Scrubbers | scrubber	2
Number of Energy Centers Constructing Wastewater Treatment Facilities | center	3
Number of energy centers | center	4
Asset Retirement Obligation	$ 759	751
Union Electric Company | Minimum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	175
Union Electric Company | Maximum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	225
Ameren Illinois Company
Loss Contingencies [Line Items]
Asset Retirement Obligation	5	$ 5
Coal Combustion Residuals Estimate | Union Electric Company | Minimum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	75
Coal Combustion Residuals Estimate | Union Electric Company | Maximum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	100
Manufactured Gas Plant
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 90
Manufactured Gas Plant | Ameren Illinois Company
Loss Contingencies [Line Items]
Number of remediation sites | site	44
Accrual for environmental loss contingencies	$ 90
Manufactured Gas Plant | Ameren Illinois Company | Minimum
Loss Contingencies [Line Items]
Estimate of possible loss	90
Manufactured Gas Plant | Ameren Illinois Company | Maximum
Loss Contingencies [Line Items]
Estimate of possible loss	150
Rush Island Energy Center | Union Electric Company
Loss Contingencies [Line Items]
Estimated capital costs to comply with preliminary court order	1,000
Rush Island Energy Center | Union Electric Company | Minimum
Loss Contingencies [Line Items]
Estimated operations and maintenance costs to comply with preliminary court order	30
Rush Island Energy Center | Union Electric Company | Maximum
Loss Contingencies [Line Items]
Estimated operations and maintenance costs to comply with preliminary court order	50
New CCR Rules Estimate
Loss Contingencies [Line Items]
Asset Retirement Obligation	103
New CCR Rules Estimate | Union Electric Company
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 103

XML

Callaway Energy Center (Insurance Disclosure) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($)
Nuclear Waste Matters [Line Items]
Decommissioning Cost	$ 7.0
Frequency of Decommissioning Cost Study	3 years
Number Of Years The Limit Of Liability And The Maximum Potential Annual Payments Are Adjusted	5 years
Number Of Weeks Of Coverage After The First Twelve Weeks Of An Outage	1
Number Of Additional Weeks After Initial Indemnity Coverage For Power Outage	1.365
Nuclear Plant | Union Electric Company
Nuclear Waste Matters [Line Items]
Estimated Nuclear Generator Repairs	$ 65.0
Replacement Power - Nuclear Electric Insurance Ltd
Nuclear Waste Matters [Line Items]
Amount Of Weekly Indemnity Coverage Commencing Twelve Weeks After Power Outage	4.5
Insurance Aggregate Maximum Coverage	490.0
Insurance Maximum Coverage per Incident	7.0
Amount Of Additional Weekly Indemnity Coverage Commencing After Initial Indemnity Coverage	3.6
Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit	490.0
Sub-Limit Of Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit For Non-Nuclear Events	328.0
Public Liability And Nuclear Worker Liability - American Nuclear Insurers
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	450.0
Insurance Maximum Coverage per Incident	0.0
Public Liability And Nuclear Worker Liability - Pool Participation
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	13,210.0
Insurance Maximum Coverage per Incident	138.0
Threshold Amount For Retrospective Insurance Assessment For Covered Loss Under Public Liability And Nuclear Worker Liability Insurance Policy	450.0
Maximum Annual Payment Per Incident At Licensed Commercial Nuclear Reactor	21.0
Public Liability
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	13,660.0
Insurance Maximum Coverage per Incident	138.0
Property Damage - Nuclear Electric Insurance Ltd
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	3,200.0
Insurance Maximum Coverage per Incident	25.0
Radiation Event
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	2,700.0
Aggregate Nuclear Power Industry Insurance Policy Limit For Losses From Terrorist Attacks Within Twelve Month Period	3,200.0
Non-Radiation Event
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	2,300.0
Aggregate Nuclear Power Industry Insurance Policy Limit For Losses From Terrorist Attacks Within Twelve Month Period	1,800.0
Property Damage European Mutual Association for Nuclear Insurance
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	$ 490.0

XML

Retirement Benefits (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total non-service cost components	$ (34)	$ (23)
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	33	27
Interest cost	38	43
Expected return on plan assets	(75)	(73)
Prior service cost (benefit)	0	0
Actuarial loss (gain)	17	14
Total non-service cost components	(20)	(16)
Net periodic benefit cost (income)	13	11
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	6	4
Interest cost	8	10
Expected return on plan assets	(20)	(20)
Prior service cost (benefit)	(1)	(1)
Actuarial loss (gain)	(1)	(2)
Total non-service cost components	(14)	(13)
Net periodic benefit cost (income)	$ (8)	$ (9)

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Retirement Benefits (Summary of Benefit Plan Costs Incurred) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ 13	$ 11
Pension Plan | Union Electric Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	6	4
Pension Plan | Ameren Illinois Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	8	7
Pension Plan | Other Affiliated Entities And Intercompany Eliminations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(1)	0
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(8)	(9)
Other Postretirement Benefit Plan, Defined Benefit | Union Electric Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(1)	(1)
Other Postretirement Benefit Plan, Defined Benefit | Ameren Illinois Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(7)	(8)
Other Postretirement Benefit Plan, Defined Benefit | Other Affiliated Entities And Intercompany Eliminations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ 0	$ 0

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Retirement Benefits (Narrative) (Details) $ in Millions	Dec. 31, 2020 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan estimated future employer contributions over next five years	$ 60

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Income Taxes Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21.00%	21.00%
Amortization of deferred investment tax credit	(1.00%)	0.00%
Amortization of excess deferred taxes	(9.00%)	(9.00%)
Depreciation differences	0.00%	(1.00%)
Renewable and other tax credits	(6.00%)	0.00%
State tax	6.00%	6.00%
Stock-based compensation	(1.00%)	(5.00%)
Effective income tax rate	10.00%	12.00%
Union Electric Company
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21.00%	21.00%
Amortization of deferred investment tax credit	(1.00%)	(1.00%)
Amortization of excess deferred taxes	(17.00%)	(15.00%)
Depreciation differences	1.00%	0.00%
Renewable and other tax credits	(11.00%)	0.00%
State tax	3.00%	3.00%
Stock-based compensation	0.00%	0.00%
Effective income tax rate	(4.00%)	8.00%
Ameren Illinois Company
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21.00%	21.00%
Amortization of deferred investment tax credit	0.00%	0.00%
Amortization of excess deferred taxes	(2.00%)	(3.00%)
Depreciation differences	(1.00%)	(1.00%)
Renewable and other tax credits	0.00%	0.00%
State tax	7.00%	7.00%
Stock-based compensation	0.00%	0.00%
Effective income tax rate	25.00%	24.00%

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Supplemental Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Supplemental Information [Abstract]
Payables for purchased receivables	$ 31		$ 28
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred Compensation Liability, Classified, Noncurrent	90		90
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount	5	$ 8
Deferred Compensation Liability, Classified, Noncurrent	$ 90		$ 90
January 1, 2021 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	38 months
Performance Shares | January 1, 2021 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	293,058
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Fair Value	$ 25
Stock Issued During Period Percentage Conversion Of Units, Low End	0.00%
Stock Issued During Period Percentage Conversion Of Units, High End	200.00%
Performance Shares | Market performance measures achievement | January 1, 2021 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	251,177
Performance Shares | Renewable generation and energy storage installation targets | January 1, 2021 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	41,881
Restricted Stock Units (RSUs) | January 1, 2021 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	125,562
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Fair Value	$ 10

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Supplemental Information (Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	$ 6	$ 139
Restricted cash included in “Other current assets”	134	17
Restricted cash included in “Other assets”	24	141
Restricted cash included in “Nuclear decommissioning trust fund”	8	4
Total cash, cash equivalents, and restricted cash	172	301	$ 203	$ 176
Union Electric Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	1	136
Restricted cash included in “Other current assets”	3	5
Restricted cash included in “Other assets”	0	0
Restricted cash included in “Nuclear decommissioning trust fund”	8	4
Total cash, cash equivalents, and restricted cash	12	145	24	39
Ameren Illinois Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	0	0
Restricted cash included in “Other current assets”	125	6
Restricted cash included in “Other assets”	24	141
Restricted cash included in “Nuclear decommissioning trust fund”	0	0
Total cash, cash equivalents, and restricted cash	$ 149	$ 147	$ 140	$ 125

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Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 50	$ 17
Bad debt expense	4	3
Net write-offs	(7)	(1)
End of period	47	19
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	16	7
Bad debt expense	1	2
Net write-offs	(2)	(1)
End of period	15	8
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	34	10
Bad debt expense	3	1
Net write-offs	(5)	0
End of period	$ 32	$ 11

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Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including wind generation expenditures	$ 271	$ 235
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund	22	(111)
Issuance of common stock for stock-based compensation	33	38
Nuclear Fuel [Member]
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including wind generation expenditures	0	7
Union Electric Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including wind generation expenditures	141	97
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund	22	(111)
Issuance of common stock for stock-based compensation	0	0
Union Electric Company | Nuclear Fuel [Member]
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including wind generation expenditures	0	7
Ameren Illinois Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including wind generation expenditures	139	127
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund	0	0
Issuance of common stock for stock-based compensation	0	0
Ameren Illinois Company | Nuclear Fuel [Member]
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including wind generation expenditures	$ 0	$ 0

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Supplemental Information (Schedule of Asset Retirement Obligations) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	$ 756
Asset Retirement Obligation, Liabilities Incurred	10
Liabilities settled	(3)
Accretion	8
Change in estimates	(7)
Asset Retirement Obligation, Ending Balance	764
Other current liabilities	392	$ 407
Union Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	751
Asset Retirement Obligation, Liabilities Incurred	10
Liabilities settled	(3)
Accretion	8
Change in estimates	(7)
Asset Retirement Obligation, Ending Balance	759
Other current liabilities	116	123
Ameren Illinois Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	5
Asset Retirement Obligation, Liabilities Incurred	0
Liabilities settled	0
Accretion	0
Change in estimates	0
Asset Retirement Obligation, Ending Balance	5
Other current liabilities	207	221
Asset Retirement Obligation Balance
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Other current liabilities	$ 59	$ 60

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Supplemental Information (Schedule Of Excise Taxes) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounting Policies [Line Items]
Excise tax expense	$ 70	$ 65
Union Electric Company
Accounting Policies [Line Items]
Excise tax expense	31	30
Ameren Illinois Company
Accounting Policies [Line Items]
Excise tax expense	$ 39	$ 35

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Supplemental Information (Earnings Per Share) (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share Reconciliation [Abstract]
Weighted-average Common Shares Outstanding – Basic	254,400,000	246,400,000
Assumed settlement of performance share units and restricted stock units	1,500,000	1,100,000
Dilutive effect of forward sale agreement	0	600,000
Weighted-average Common Shares Outstanding – Diluted	255,900,000	248,100,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	0	0

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Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 1,566	$ 1,440
Net income (loss) attributable to common shareholders	233	146
Capital expenditures	887	636
Wind generation expenditures	(193)	0
Union Electric Company
Segment Reporting Information [Line Items]
Revenues	704	680
Net income (loss) attributable to common shareholders	47	(10)
Wind generation expenditures	(193)	0
Ameren Illinois Company
Segment Reporting Information [Line Items]
Revenues	823	723
Net income (loss) attributable to common shareholders	149	120
Capital expenditures	337	324
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
Revenues	695	670
Net income (loss) attributable to common shareholders	47	(10)
Capital expenditures	534	278
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	411	389
Net income (loss) attributable to common shareholders	46	37
Capital expenditures	157	123
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	347	271
Net income (loss) attributable to common shareholders	75	55
Capital expenditures	48	61
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
Revenues	113	110
Net income (loss) attributable to common shareholders	47	47
Capital expenditures	141	170
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	411	390
Net income (loss) attributable to common shareholders	46	37
Capital expenditures	157	123
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	347	271
Net income (loss) attributable to common shareholders	75	55
Capital expenditures	48	61
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Revenues	65	62
Net income (loss) attributable to common shareholders	28	28
Capital expenditures	132	140
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue Not from Contract with Customer	(26)	(24)
Capital expenditures	6	1
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Revenue Not from Contract with Customer	(9)	(10)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenue Not from Contract with Customer	0	(1)
Intersegment Eliminations | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenue Not from Contract with Customer	0	0
Intersegment Eliminations | Ameren Transmission
Segment Reporting Information [Line Items]
Revenue Not from Contract with Customer	(17)	(13)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Revenues	(16)	(12)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Revenues	(16)	(12)
Other
Segment Reporting Information [Line Items]
Net income (loss) attributable to common shareholders	18	17
Capital expenditures	$ 1	$ 3

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Segment Information (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 1,566	$ 1,440
Revenues	1,566	1,440
Revenues from alternative revenue programs	53	66
Other revenues not from contracts with customers	2	10
Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(10)	(3)
Other revenues not from contracts with customers	(2)	8
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	61	46
Other revenues not from contracts with customers	3	1
Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	3	11
Other revenues not from contracts with customers	1	1
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(1)	12
Other revenues not from contracts with customers	0	0
Electricity
Disaggregation of Revenue [Line Items]
Revenues	1,156	1,120
Revenues	1,156	1,120
Electricity | Residential
Disaggregation of Revenue [Line Items]
Revenues	541	517
Electricity | Commercial
Disaggregation of Revenue [Line Items]
Revenues	348	347
Electricity | Industrial
Disaggregation of Revenue [Line Items]
Revenues	86	88
Electricity | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	181	168
Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	410	320
Revenues	410	320
Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	285	246
Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	79	67
Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	15	4
Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	31	3
Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	823	723
Revenues	823	723
Revenues from alternative revenue programs	63	67
Other revenues not from contracts with customers	4	2
Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Revenues	480	433
Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues	196	180
Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues	48	38
Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	99	72
Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	61	46
Other revenues not from contracts with customers	3	1
Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	3	11
Other revenues not from contracts with customers	1	1
Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(1)	10
Other revenues not from contracts with customers	0	0
Ameren Illinois Company | Electricity
Disaggregation of Revenue [Line Items]
Revenues	476	452
Ameren Illinois Company | Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	347	271
Operating Segments | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	695	670
Revenues	704	680
Operating Segments | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	411	389
Revenues	411	390
Operating Segments | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	347	271
Revenues	347	271
Operating Segments | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	113	110
Revenues	130	123
Operating Segments | Electricity | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	641	631
Operating Segments | Electricity | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Revenues	312	297
Operating Segments | Electricity | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues	216	221
Operating Segments | Electricity | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues	52	53
Operating Segments | Electricity | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	61	60
Operating Segments | Electricity | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	411	390
Operating Segments | Electricity | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenues	229	220
Operating Segments | Electricity | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenues	132	126
Operating Segments | Electricity | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenues	34	35
Operating Segments | Electricity | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	16	9
Operating Segments | Electricity | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electricity | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electricity | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electricity | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electricity | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0
Operating Segments | Electricity | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	130	123
Operating Segments | Electricity | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electricity | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electricity | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electricity | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	130	123
Operating Segments | Natural Gas | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	63	49
Operating Segments | Natural Gas | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Revenues	34	33
Operating Segments | Natural Gas | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues	15	13
Operating Segments | Natural Gas | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues	1	1
Operating Segments | Natural Gas | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	13	2
Operating Segments | Natural Gas | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural Gas | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural Gas | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural Gas | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural Gas | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0
Operating Segments | Natural Gas | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	347	271
Operating Segments | Natural Gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	251	213
Operating Segments | Natural Gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	64	54
Operating Segments | Natural Gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	14	3
Operating Segments | Natural Gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	18	1
Operating Segments | Natural Gas | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural Gas | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural Gas | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural Gas | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural Gas | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	411	390
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	347	271
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	65	62
Operating Segments | Ameren Illinois Company | Electricity | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	411	390
Operating Segments | Ameren Illinois Company | Electricity | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenues	229	220
Operating Segments | Ameren Illinois Company | Electricity | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenues	132	126
Operating Segments | Ameren Illinois Company | Electricity | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenues	34	35
Operating Segments | Ameren Illinois Company | Electricity | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	16	9
Operating Segments | Ameren Illinois Company | Electricity | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	81	74
Operating Segments | Ameren Illinois Company | Electricity | Ameren Illinois Transmission | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Ameren Illinois Company | Electricity | Ameren Illinois Transmission | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Ameren Illinois Company | Electricity | Ameren Illinois Transmission | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Ameren Illinois Company | Electricity | Ameren Illinois Transmission | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	81	74
Operating Segments | Ameren Illinois Company | Natural Gas | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	347	271
Operating Segments | Ameren Illinois Company | Natural Gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	251	213
Operating Segments | Ameren Illinois Company | Natural Gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	64	54
Operating Segments | Ameren Illinois Company | Natural Gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	14	3
Operating Segments | Ameren Illinois Company | Natural Gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	18	1
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(26)	(24)
Revenues	(26)	(24)
Intersegment Eliminations | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(9)	(10)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	(1)
Intersegment Eliminations | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0
Intersegment Eliminations | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(17)	(13)
Intersegment Eliminations | Electricity
Disaggregation of Revenue [Line Items]
Revenues	(26)	(24)
Intersegment Eliminations | Electricity | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Electricity | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Electricity | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Electricity | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(26)	(24)
Intersegment Eliminations | Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0
Intersegment Eliminations | Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	(16)	(12)
Revenues	(16)	(12)
Intersegment Eliminations | Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(16)	(12)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	$ (16)	$ (12)