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Rate And Regulatory Matters (Tables)
 12 Months Ended
Dec. 31, 2020
Public Utilities, General Disclosures [Abstract]  
Schedule Of Regulatory Assets And Liabilities
The following table presents our regulatory assets and regulatory liabilities at December 31, 2020 and 2019:
20202019
Ameren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois		Ameren
Regulatory assets:
Under-recovered FAC(a)
$48 $— $48 $— $— $— 
Under-recovered Illinois electric power costs(b)
— 4 4 — 4 4 
MTM derivative losses(c)
21 200 221 12 242 254 
IEIMA revenue requirement reconciliation adjustment(d)(e)
— — — — 17 17 
FERC revenue requirement reconciliation adjustment(f)
— 28 50 — 1 16 
Under-recovered VBA(g)
— 11 11 — — — 
Pension and postretirement benefit costs(h)
— — — 7 26 33 
Income taxes(i)
117 65 183 114 61 177 
Bad debt rider(j)
— 11 11 — — — 
Callaway costs(e)(k)
14 — 14 18 — 18 
Callaway refueling and maintenance outage costs(l)
39 — 39 — — — 
Unamortized loss on reacquired debt(m)
52 22 74 55 31 86 
Environmental cost riders(n)
— 93 93 — 127 127 
Storm costs(e)(o)
— 7 7 — 7 7 
Workers’ compensation claims(p)
4 5 9 4 7 11 
Allowance for funds used during construction for pollution control equipment(e)(q)
15 — 15 15 — 15 
Customer generation rebate program(e)(r)
— 17 17 — 1 1 
Solar rebate program(s)
5 — 5 5 — 5 
PISA(e)(t)
78 — 78 41 — 41 
RESRAM(u)
2 — 2 9 — 9 
FEJA energy-efficiency rider(e)(v)
— 283 283 — 211 211 
Other12 33 45 13 16 29 
Total regulatory assets$407 $779 $1,209 $293 $751 $1,061 
Less: current regulatory assets(60)(37)(109)(8)(57)(69)
Noncurrent regulatory assets$347 $742 $1,100 $285 $694 $992 
Regulatory liabilities:
Over-recovered FAC(a)
$10 $— $10 $39 $— $39 
Over-recovered Illinois electric power costs(b)
— 15 15 — 11 11 
Over-recovered PGA(b)
7 15 22 8 14 22 
Over-recovered VBA(g)
— — — — 8 8 
MTM derivative gains(c)
11 10 21 18 3 21 
IEIMA revenue requirement reconciliation adjustment(d)
— 22 22 — 18 18 
FERC revenue requirement reconciliation adjustment(f)
— 21 21 — 37 38 
Estimated refund for FERC complaint cases(w)
— 7 15 — 23 40 
Income taxes(i)
1,317 790 2,192 1,428 813 2,326 
Cost of removal(x)
1,027 873 1,923 1,041 827 1,884 
AROs(y)
436 — 436 303 — 303 
Pension and postretirement benefit costs(h)
198 177 375 — — — 
Pension and postretirement benefit costs tracker(z)
55 — 55 72 — 72 
Renewable energy credits and zero emission credits(aa)
— 200 200 — 155 155 
Excess income taxes collected in 2018(ab)
45 — 45 60 — 60 
Other30 21 51 30 24 54 
Total regulatory liabilities$3,136 $2,151 $5,403 $2,999 $1,933 $5,051 
Less: current regulatory liabilities(26)(88)(121)(62)(84)$(164)
Noncurrent regulatory liabilities$3,110 $2,063 $5,282 $2,937 $1,849 $4,887 
(a)Under-recovered or over-recovered fuel costs to be recovered or refunded through the FAC. Specific accumulation periods aggregate the under-recovered or over-recovered costs over four months, any related adjustments that occur over the following four months, and the recovery from, or refund to, 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)Deferral of commodity-related derivative MTM losses or gains. See Note 7 – Derivative Financial Instruments for additional information.
(d)The difference between Ameren Illinois’ electric distribution service annual revenue requirement calculated under the performance-based formula ratemaking framework and the revenue requirement included in customer rates for that year. Any under-recovery or over-recovery will be recovered from, or refunded to, customers with interest within two years.
(e)These assets earn a return at the applicable WACC.
(f)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.
(g)Under-recovered or over-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 or refunded to customers from April through December of the following year.
(h)Under-recovered or 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.
(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 changes. The regulatory liabilities represent amounts that will be refunded to customers for deferred income taxes related to depreciation differences, other tax liabilities, and the unamortized portion of investment tax credits 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 34, 26, and 42 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. Pursuant to the June 2020 ICC order in the service disconnection moratorium proceeding discussed above, Ameren Illinois’ electric distribution bad debt rider provided for the recovery of bad debt expense in 2020. The under-recovery or over-recovery for each year is recovered from, or refunded to, customers over a twelve-month period beginning June the following year.
(k)Ameren Missouri’s Callaway Energy Center operations and maintenance expenses, property taxes, and carrying costs incurred between the plant in-service date and the date the plant was reflected in rates. These costs are being amortized over the original remaining life of the energy center.
(l)In February 2020, the MoPSC issued an order approving a stipulation and agreement allowing Ameren Missouri to defer and amortize maintenance expenses related to scheduled refueling and maintenance outages at its Callaway Energy Center. Maintenance expenses are amortized over the period between refueling and maintenance outages, which has historically been approximately 18 months. Amortization began in January 2021 and will continue until the completion of the next refueling and maintenance outage.
(m)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.
(n)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.
(o)Storm costs from 2016, 2018, and 2020 deferred in accordance with the IEIMA. These costs are being amortized over five-year periods beginning in the year the storm occurred.
(p)The period of recovery will depend on the timing of actual expenditures.
(q)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 2033.
(r)Costs associated with Ameren Illinois’ customer generation rebate program. Costs are amortized over a 15-year period, beginning in the year rebates are paid.
(s)Costs associated with Ameren Missouri’s solar rebate program. The amortization period for these assets will be determined in a future electric service regulatory rate review.
(t)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 after September 1, 2018, and not included in base rates. Accumulated PISA deferrals are added to rate base prospectively and amortized over a period of 20 years following a regulatory rate review.
(u)Costs associated with Ameren Missouri’s compliance with the state of Missouri’s renewable energy standard. Costs incurred over a twelve-month period beginning each August are amortized over a twelve-month period beginning February the following year.
(v)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 6 to 13 years.
(w)The 2020 balances represent the estimated refunds to transmission customers related to the May 2020 FERC order in the November 2013 FERC complaint case. The 2019 balances represent the estimated refunds to transmission customers related to the November 2019 FERC order in the November 2013 FERC complaint case. See further discussion of the FERC ROE complaint cases above.
(x)Estimated funds collected from customers to pay for the future removal cost of property, plant, and equipment retired from service, net of salvage.
(y)The ARO regulatory liability includes the nuclear decommissioning trust fund balance (December 31, 2020 - $982 million), net of recoverable removal costs for AROs (December 31, 2020 - $546 million). See Note 1 – Summary of Significant Accounting Policies – Asset Retirement Obligations.
(z)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 costs incurred prior to 2019, the weighted-average remaining amortization period is four years. For costs incurred during 2019 and after, the amortization period will be determined in a future electric service regulatory rate review.
(aa)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.
(ab)The excess amount collected in rates related to the TCJA from January 1, 2018, through July 31, 2018. The regulatory liability is being amortized over a three-year period, which began in April 2020.