Rate And Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2023

Public Utilities, General Disclosures [Abstract]

Schedule of Regulatory Frameworks and Significant Recovery Mechanisms

The following table presents the regulatory frameworks and significant regulatory recovery mechanisms for each of Ameren’s rate-regulated businesses, which are discussed in more detail below:

	Ameren Missouri	Ameren Illinois’ electric distribution business	Ameren Illinois’ natural gas delivery business	Ameren Illinois’ and ATXI’s electric transmission businesses
Regulatory framework	•Historical test year ratemaking •Natural gas revenues for residential customers adjusted for sales volume deviations resulting from weather through the WNAR	•MYRP(a) •Initial rates based on future test years •Revenues decoupled from sales volumes	•Future test year ratemaking •Revenues for residential and small nonresidential customers decoupled from sales volumes through the VBA	•Formula ratemaking •Initial rates based on future test year •Revenues decoupled from sales volumes
Regulatory mechanisms	•PISA Riders: •RESRAM •FAC •MEEIA •PGA •WNAR Trackers: •Pension and postretirement benefit costs •Certain excess deferred income taxes •Renewable energy standard costs •Property taxes •Production and investment tax credits or proceeds from the sale of certain tax credits allowed under the IRA	•Electric distribution service and energy-efficiency revenue requirement reconciliation adjustments(b) Riders: •Power procurement •Transmission services •Renewable energy credit compliance •Zero emission credits •Certain environmental costs •Bad debt write-offs •Costs of certain asbestos-related claims	Riders: •QIP(c) •PGA •VBA •Energy-efficiency program costs •Certain environmental costs •Bad debt write-offs •Invested capital taxes	•Revenue requirement reconciliation adjustment

(a)Ameren Illinois used the IEIMA performance-based formula ratemaking framework to establish annual electric distribution customer rates effective through 2023. In December 2023, the ICC approved an MYRP to establish rates effective 2024 through 2027. See below for additional information regarding the MYRP approved in December 2023.

(b)Reconciliation adjustments under an MYRP are subject to a reconciliation cap which limits annual adjustment to 105%. See below for additional information regarding the reconciliation cap.

(c)The QIP expired in December 2023. Reconciliation hearings to determine the accuracy and prudence of natural gas capital investments recovered under the QIP from 2020 to 2023 are ongoing.

Schedule of Solar Projects

The following table provides information with respect to each agreement:

	Huck Finn Solar Project(a)(b)	Boomtown Solar Project(b)(c)	Split Rail Solar Project(d)	Cass County Solar Project(c)	Vandalia Solar Project(d)	Bowling Green Solar Project(d)
Agreement type	Build-transfer	Build-transfer	Build-transfer(e)	Development-transfer(e)(f)	Self-build(e)(g)	Self-build(e)(g)
Facility size	200-MW	150-MW	300-MW	150-MW	50-MW	50-MW
Status of MoPSC CCN	Approved February 2023	Approved April 2023	Filed June 2023(h)	Filed June 2023(h)	Filed June 2023(h)	Filed June 2023(h)
Status of FERC approval of acquisition	Received March 2023	Received October 2023	Expect to request by mid-2024	Not applicable	Not applicable	Not applicable
Earliest completion date(i)	Fourth quarter 2024	Fourth quarter 2024	Mid-2026	Fourth quarter 2024	Fourth quarter 2025	First quarter 2026

(a)The Huck Finn Solar Project is expected to support Ameren Missouri’s compliance with the state of Missouri’s renewable energy standard. Investments in the project will be eligible for recovery under the RESRAM.

(b)These projects collectively represent approximately $0.65 billion of expected capital expenditures.

(c)The Boomtown and Cass County solar projects are expected to support Ameren Missouri’s transition to renewable energy generation and serve customers under the Renewable Solutions Program discussed below.

(d)These solar projects are expected to support Ameren Missouri’s transition to renewable energy generation.

(e)These projects, and applicable agreements, are subject to the issuance of a CCN by the MoPSC.

(f)Ameren Missouri entered into an agreement to acquire the Cass County Solar Project, which includes project design, land rights, and engineering, procurement, and construction agreements for a solar generation facility. Ameren Missouri will construct the facility after obtaining a CCN from the MoPSC and acquiring the project. Acquisition of the project is expected by mid-2024.

(g)Ameren Missouri entered into engineering, procurement, and construction agreements to construct these solar projects.

(h)In February 2024, Ameren Missouri, the MoPSC staff, and the MoOPC filed a nonunanimous stipulation and agreement requesting the MoPSC approve Ameren Missouri’s requests for CCNs for the Split Rail, Vandalia, and Bowling Green solar projects. The stipulation and agreement also requests MoPSC approval of the CCN request for the Cass County Solar Project conditioned upon the facility supporting the Renewable Solutions Program discussed below and full subscription of the portion of the program supported by this facility, subject to certain other terms and conditions. The remaining intervenors did not object to the agreement. Ameren Missouri expects a decision by the MoPSC in March 2024.

(i)Expected completion dates are dependent on the timing of regulatory approvals, among other things.

Schedule of MYRP details

The following table presents the approved revenue requirements, ROE, capital structure common equity percentage, and annual rate base in the ICC’s December 2023 order, as well as the proposed revenue requirements and annual rate base amounts in Ameren Illinois’ February 2024 rehearing request filing:

Year	Revenue Requirement (in millions)	ROE	Capital Structure Common Equity Percentage	Annual Rate Base (in billions)
ICC’s December 2023 MYRP Order:
2024	$1,162	8.72%	50%	$3.9
2025	$1,210	8.72%	50%	$3.9
2026	$1,242	8.72%	50%	$3.9
2027	$1,255	8.72%	50%	$3.9
Ameren Illinois’ February 2024 Rehearing Request Filing:
2024	$1,214	(a)	50%	$4.2
2025	$1,300	(a)	50%	$4.5
2026	$1,371	(a)	50%	$4.7
2027	$1,420	(a)	50%	$4.9

(a)The ROE is under appeal as discussed above.

Schedule Of Regulatory Assets And Liabilities

The following table presents our regulatory assets and regulatory liabilities at December 31, 2023 and 2022:

	2023						2022
	Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois		Ameren
Regulatory assets:
Under-recovered FAC(a)	$	72	$	—	$	72	$	140	$	—	$	140
Under-recovered Illinois electric power costs(b)	—		10		10		—		33		33
Under-recovered PGA(b)(c)	6		—		6		23		—		23
MTM derivative losses(d)	25		143		168		68		68		136
IEIMA revenue requirement reconciliation adjustment(e)(f)	—		239		239		—		134		134
FERC revenue requirement reconciliation adjustment(g)	—		25		54		—		11		33
Under-recovered VBA(h)	—		49		49		—		—		—
Income taxes(i)	126		78		207		111		72		185
Bad debt rider(j)	—		43		43		—		5		5
Callaway refueling and maintenance outage costs(k)	37		—		37		33		—		33
Unamortized loss on reacquired debt(l)	45		5		50		47		7		54
Environmental cost riders(m)	—		50		50		—		64		64
Storm costs(f)(n)	—		27		27		—		14		14
Allowance for funds used during construction for pollution control equipment(f)(o)	10		—		10		11		—		11
Customer generation rebate program(f)(p)	—		54		54		—		50		50
PISA(f)(q)	386		—		386		320		—		320
RESRAM(r)	48		—		48		6		—		6
Certain Meramec Energy Center costs(s)	39		—		39		51		—		51
FEJA energy-efficiency rider(f)(t)	—		500		500		—		416		416
Property tax tracker(u)	13		—		13		3		—		3
Other	49		64		113		35		34		69
Total regulatory assets	$	856	$	1,287	$	2,175	$	848	$	908	$	1,780
Less: current regulatory assets	(101)		(252)		(365)		(254)		(87)		(354)
Noncurrent regulatory assets	$	755	$	1,035	$	1,810	$	594	$	821	$	1,426
Regulatory liabilities:
Over-recovered Illinois electric power costs(b)	—		36		36		—		—		—
Over-recovered PGA(b)	7		33		40		—		10		10
MTM derivative gains(d)	19		3		22		51		40		91
Income taxes(i)	999		724		1,809		1,095		749		1,931
Cost of removal(v)	1,098		1,038		2,186		1,064		989		2,091
AROs(w)	524		—		524		365		—		365
Bad debt rider(j)	—		7		7		—		21		21
Pension and postretirement benefit costs(x)	202		144		346		242		162		404
Pension and postretirement benefit costs tracker(y)	111		—		111		60		—		60
Renewable energy credits and zero emission credits(z)	—		489		489		—		373		373
Other	14		15		29		64		33		99
Total regulatory liabilities	$	2,974	$	2,489	$	5,599	$	2,941	$	2,377	$	5,445
Less: current regulatory liabilities	(15)		(71)		(87)		(70)		(64)		(136)
Noncurrent regulatory liabilities	$	2,959	$	2,418	$	5,512	$	2,871	$	2,313	$	5,309

(a)Under-recovered fuel and purchased power costs to be recovered through the FAC. Specific accumulation periods aggregate the under-recovered costs over four months, any related adjustments that occur over the following four months, and the recovery from customers that occurs over the next eight months.

(b)Under-recovered or over-recovered costs from utility customers. Amounts will be recovered from, or refunded to, customers within one year of the deferral.

(c)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 had under-recovered costs under its PGA clause of $53 million. Pursuant to an October 2021 MoPSC order, the collection period for Ameren Missouri’s cumulative PGA under-recovery as of August 2021, which included the February 2021 under-recovery, was extended from 12 months to 36 months, beginning November 2021.

(d)Deferral of commodity-related derivative MTM losses or gains. See Note 7 – Derivative Financial Instruments for additional information.

(e)The difference between Ameren Illinois’ electric distribution service annual revenue requirement calculated under the IEIMA performance-based formula ratemaking framework and the revenue requirement included in customer rates for that year. The under-recovery will be recovered from customers with a return at the applicable WACC within two years.

(f)These assets earn a return at the applicable WACC.

(g)Ameren Illinois’ and ATXI’s annual revenue requirement reconciliation calculated pursuant to the FERC’s electric transmission formula ratemaking framework. Any under-recovery or over-recovery will be recovered from, or refunded to, customers within two years.

(h)Under-recovered natural gas revenue caused by sales volume deviations from weather normalized sales approved by the ICC in rate regulatory reviews. Each year’s amount will be recovered from customers from April through December of the following year.

(i)The regulatory assets represent amounts that will be recovered from customers for deferred income taxes related to the equity component of allowance for funds used during construction and the effects of tax rate increases. The regulatory liabilities represent amounts that will be refunded to customers for excess deferred income taxes related to depreciation differences, other tax liabilities, and the unamortized portion of investment tax credits all recorded at rates in excess of current statutory rates. Amounts associated with the equity component of allowance for funds used during construction and the unamortized portion of investment tax credits will be amortized over the expected life of the related assets. For net regulatory liabilities related to deferred income taxes recorded at rates other than the current statutory rate, the weighted-average remaining amortization periods at Ameren, Ameren Missouri, and Ameren Illinois are 36, 28, and 43 years.

(j)A rider for the difference between the level of bad debt write-offs, net of any subsequent recoveries, incurred by Ameren Illinois and the level of such costs included in electric distribution and natural gas delivery service rates. Under-recovered or over-recovered costs for each year are collected from, or refunded to, customers over a twelve-month period beginning in June of the following year.

(k)Maintenance expenses related to scheduled refueling and maintenance outages at Ameren Missouri’s Callaway Energy Center. Amounts are amortized over the period between refueling and maintenance outages, which has historically been approximately 18 months.

(l)Losses related to reacquired debt. These amounts are being amortized over the lives of the related new debt issuances or the original lives of the old debt issuances if no new debt was issued.

(m)The recoverable portion of accrued environmental site liabilities that will be collected from electric and natural gas customers through ICC-approved cost recovery riders. The period of recovery will depend on the timing of remediation expenditures. See Note 14 – Commitments and Contingencies for additional information.

(n)Storm costs from 2020 through 2023 deferred in accordance with the IEIMA. These costs are being amortized over five-year periods beginning in the year the storm occurred.

(o)The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to record an allowance for funds used during construction for pollution control equipment at its Sioux Energy Center until the cost of that equipment was included in customer rates beginning in 2011. These costs are being amortized over the expected life of the Sioux Energy Center, currently through 2030.

(p)Costs associated with Ameren Illinois’ customer generation rebate program. Costs are amortized over a 15-year period, beginning in the year rebates are paid.

(q)Under the PISA, Ameren Missouri is permitted 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. Accumulated PISA deferrals, which also earn a return at the applicable WACC, are added to rate base prospectively and amortized over a period of 20 years following a regulatory rate review.

(r)Under-recovered costs associated with Ameren Missouri’s compliance with the state of Missouri’s renewable energy standard. Under-recovered or over-recovered costs are aggregated over a twelve-month period beginning each August and are amortized over a twelve-month period beginning in February of the following year.

(s)Certain costs associated with the Meramec Energy Center, which were authorized for recovery by a December 2021 MoPSC electric rate order. These costs are being collected over five years beginning in February 2022.

(t)The electric energy-efficiency investments are being amortized over their weighted-average useful lives beginning in the period in which they were made, with current remaining amortization periods ranging from three to 12 years.

(u)A regulatory recovery mechanism for the difference between actual property taxes incurred by Ameren Missouri and the related taxes included in customer rates. The period of recovery, or refund, varies based on MoPSC approval in a regulatory rate review. Amounts accumulated through 2022 are being collected over two years beginning July 2023. The amortization period for amounts accumulated after 2022 will be determined in a future regulatory rate review.

(v)Estimated funds collected from customers to pay for the future removal cost of property, plant, and equipment when retired from service, net of salvage.

(w)The ARO regulatory liability includes the nuclear decommissioning trust fund balance ($1,150 million and $958 million at December 31, 2023 and 2022, respectively), net of recoverable removal costs for AROs ($626 million and $593 million at December 31, 2023 and 2022, respectively). See Note 1 – Summary of Significant Accounting Policies – Asset Retirement Obligations and Removal Costs.

(x)Over-recovered costs are being amortized in proportion to the recognition of prior service costs (credits) and actuarial losses (gains) attributable to Ameren’s pension plan and postretirement benefit plans. See Note 10 – Retirement Benefits for additional information.

(y)A regulatory recovery mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri and the level of such costs included in customer rates. The period of refund varies based on MoPSC approval in a regulatory rate review. For electric and natural gas related costs incurred prior to 2023 and 2022, respectively, the weighted-average remaining amortization period is three years. For electric and natural gas related costs incurred after 2023 and 2022, respectively, the amortization period will be determined in a future regulatory rate review.

(z)Funds collected for the purchase of renewable energy credits and zero emission credits through IPA procurements. The balance will be amortized as the credits are purchased. Pursuant to the CEJA, if funds collected from customers are not used to procure renewable energy credits, they would be refunded to customers pursuant to a reconciliation proceeding, the first of which was initiated in August 2023. Based on amounts collected from customers and renewable energy credit purchases under contract, the August 2023 reconciliation proceeding did not result in refunds to customers.