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Rate And Regulatory Matters (Schedule Of Regulatory Assets And Liabilities) (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Feb. 28, 2021
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 1,780 | $ 1,608 |
Current regulatory assets | (354) | (319) |
Regulatory Assets, Noncurrent | 1,426 | 1,289 |
Regulatory Liabilities | 5,445 | 5,961 |
Current regulatory liabilities | (136) | (113) |
Regulatory Liability, Noncurrent | 5,309 | 5,848 |
Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 848 | 650 |
Current regulatory assets | (254) | (127) |
Regulatory Assets, Noncurrent | 594 | 523 |
Regulatory Liabilities | 2,941 | 3,411 |
Current regulatory liabilities | (70) | (57) |
Regulatory Liability, Noncurrent | $ 2,871 | 3,354 |
PISA Deferral Percentage | 85.00% |  |
Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 908 | 932 |
Current regulatory assets | (87) | (180) |
Regulatory Assets, Noncurrent | 821 | 752 |
Regulatory Liabilities | 2,377 | 2,428 |
Current regulatory liabilities | (64) | (54) |
Regulatory Liability, Noncurrent | 2,313 | 2,374 |
Under-recovered FAC |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 140 | 47 |
Under-recovered FAC | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 140 | 47 |
Under-recovered FAC | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 0 | 0 |
Under-recovered Illinois electric power costs |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 33 | 3 |
Under-recovered Illinois electric power costs | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 0 | 0 |
Under-recovered Illinois electric power costs | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 33 | 3 |
Under-recovered PGA |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 23 | 163 |
Under-recovered PGA | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 23 | 49 | $ 53
Under-recovered PGA | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 0 | 114 | $ 221
Regulatory Asset, Amortization Period | 18 months |  |
MTM derivative losses |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 136 | 202 |
MTM derivative losses | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 68 | 77 |
MTM derivative losses | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 68 | 125 |
IEIMA revenue requirement reconciliation adjustment |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 134 | 42 |
IEIMA revenue requirement reconciliation adjustment | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 0 | 0 |
IEIMA revenue requirement reconciliation adjustment | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 134 | 42 |
Amortization Period | 2 years |  |
FERC revenue requirement reconciliation adjustment |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 33 | 43 |
Amortization Period | 2 years |  |
FERC revenue requirement reconciliation adjustment | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 0 | 0 |
FERC revenue requirement reconciliation adjustment | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 11 | 18 |
Under-recovered VBA |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 0 | 17 |
Under-recovered VBA | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 0 | 0 |
Under-recovered VBA | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 0 | 17 |
Income taxes |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 185 | 185 |
Regulatory Liabilities | $ 1,931 | 2,066 |
Weighted-Average Amortization Period | 38 years |  |
Income taxes | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 111 | 115 |
Regulatory Liabilities | $ 1,095 | 1,208 |
Weighted-Average Amortization Period | 31 years |  |
Income taxes | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 72 | 69 |
Regulatory Liabilities | $ 749 | 770 |
Weighted-Average Amortization Period | 44 years |  |
Callaway refueling and maintenance outage costs |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 33 | 14 |
Callaway refueling and maintenance outage costs | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 33 | 14 |
Regulatory Asset, Amortization Period | 18 months |  |
Callaway refueling and maintenance outage costs | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 0 | 0 |
Unamortized loss on reacquired debt |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 54 | 63 |
Unamortized loss on reacquired debt | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 47 | 50 |
Unamortized loss on reacquired debt | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 7 | 13 |
Environmental cost riders |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 64 | 70 |
Environmental cost riders | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 0 | 0 |
Environmental cost riders | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 64 | 70 |
Storm costs |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 14 | 17 |
Storm costs | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 0 | 0 |
Storm costs | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 14 | 17 |
Allowance for funds used during construction for pollution control equipment |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 11 | 13 |
Allowance for funds used during construction for pollution control equipment | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 11 | 13 |
Allowance for funds used during construction for pollution control equipment | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 0 | 0 |
Customer generation rebate program |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 50 | 47 |
Customer generation rebate program | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 0 | 0 |
Customer generation rebate program | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 50 | 47 |
PISA |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 320 | 244 |
PISA | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 320 | 244 |
Amortization Period | 20 years |  |
Regulatory Asset, Amortization Period | 20 years |  |
PISA | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 0 | 0 |
Certain Meramec Energy Center costs |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 51 | 0 |
Certain Meramec Energy Center costs | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 51 | 0 |
Regulatory Asset, Amortization Period | 5 years |  |
Certain Meramec Energy Center costs | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | $ 0 | 0 |
FEJA energy-efficiency rider |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 416 | 350 |
FEJA energy-efficiency rider | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 0 | 0 |
FEJA energy-efficiency rider | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 416 | 350 |
Other regulatory assets |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 83 | 88 |
Other regulatory assets | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 44 | 41 |
Other regulatory assets | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Assets | 39 | 47 |
Over-recovered FAC |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 4 | 19 |
Over-recovered FAC | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | $ 4 | 19 |
Accumulation Period | 4 months |  |
Amortization Period | 8 months |  |
Over-recovered FAC | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | $ 0 | 0 |
Over-recovered Illinois electric power costs |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 0 | 13 |
Over-recovered Illinois electric power costs | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 0 | 0 |
Over-recovered Illinois electric power costs | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | $ 0 | 13 |
Amortization Period | 1 year |  |
Over-recovered PGA |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | $ 10 | 1 |
Over-recovered PGA | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 0 | 0 |
Over-recovered PGA | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 10 | 1 |
MTM derivative gains |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 91 | 91 |
MTM derivative gains | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 51 | 50 |
MTM derivative gains | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 40 | 41 |
Cost of removal |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 2,091 | 1,988 |
Cost of removal | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 1,064 | 1,028 |
Cost of removal | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 989 | 929 |
AROs |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 365 | 603 |
AROs | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 365 | 603 |
AROs | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 0 | 0 |
Bad debt rider |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 21 | 19 |
Bad debt rider | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 0 | 0 |
Bad debt rider | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 21 | 19 |
Pension and postretirement benefit costs |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 404 | 791 |
Pension and postretirement benefit costs | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 242 | 399 |
Pension and postretirement benefit costs | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 162 | 392 |
Pension and postretirement benefit costs tracker |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 60 | 28 |
Pension and postretirement benefit costs tracker | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | $ 60 | 28 |
Regulatory Liability, Amortization Period | 4 years |  |
Pension and postretirement benefit costs tracker | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | $ 0 | 0 |
Renewable energy credits and zero emission credits |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 373 | 246 |
Renewable energy credits and zero emission credits | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 0 | 0 |
Renewable energy credits and zero emission credits | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 373 | 246 |
RESRAM |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 2 | 19 |
RESRAM | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 2 | 19 |
RESRAM | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 0 | 0 |
Excess income taxes collected in 2018 |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 7 | 25 |
Excess income taxes collected in 2018 | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 7 | 25 |
Excess income taxes collected in 2018 | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 0 | 0 |
Other regulatory liabilities |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 86 | 52 |
Other regulatory liabilities | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | 51 | 32 |
Other regulatory liabilities | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | $ 33 | 17 |
FAC adjustments | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Accumulation Period | 4 months |  |
Asset Retirement Obligation - Nuclear decommissioning trust fund balance | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | $ 958 | 1,159 |
Asset Retirement Obligation - removal costs | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | $ 593 | $ 556 |
Minimum | Under-recovered PGA | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Asset, Amortization Period | 12 months |  |
Minimum | FEJA energy-efficiency rider | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Asset, Amortization Period | 4 years |  |
Maximum | Under-recovered PGA | Union Electric Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Asset, Amortization Period | 36 months |  |
Maximum | FEJA energy-efficiency rider | Ameren Illinois Company |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Asset, Amortization Period | 12 years |  |

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