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Rate And Regulatory Matters (Schedule Of Regulatory Assets And Liabilities) (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2025 | Dec. 31, 2024
Regulatory assets: |  |
Less: current regulatory assets | $ (387,000,000) | $ (366,000,000)
Noncurrent regulatory assets | 2,524,000,000 | 2,397,000,000
Regulatory liabilities: |  |
Noncurrent regulatory liabilities | 6,255,000,000 | 5,897,000,000
Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 1,631,000,000 | 1,432,000,000
Less: current regulatory assets | (181,000,000) | (66,000,000)
Noncurrent regulatory assets | 1,450,000,000 | 1,366,000,000
Regulatory liabilities: |  |
Total regulatory liabilities | 3,347,000,000 | 3,213,000,000
Less: current regulatory liabilities | (23,000,000) | (37,000,000)
Noncurrent regulatory liabilities | $ 3,324,000,000 | $ 3,176,000,000
PISA deferral percentage | 85.00% |
Ameren Missouri | Rush Island Energy Center |  |
Regulatory liabilities: |  |
Regulatory asset, amortization period |  | 15 years
Amortization of regulatory asset |  | $ 15
Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | $ 1,248,000,000 | 1,292,000,000
Less: current regulatory assets | (189,000,000) | (281,000,000)
Noncurrent regulatory assets | 1,059,000,000 | 1,011,000,000
Regulatory liabilities: |  |
Total regulatory liabilities | 2,907,000,000 | 2,652,000,000
Less: current regulatory liabilities | (132,000,000) | (79,000,000)
Noncurrent regulatory liabilities | 2,775,000,000 | 2,573,000,000
Ameren (parent) |  |
Regulatory assets: |  |
Total regulatory assets | 2,911,000,000 | 2,763,000,000
Less: current regulatory assets | (387,000,000) | (366,000,000)
Noncurrent regulatory assets | 2,524,000,000 | 2,397,000,000
Regulatory liabilities: |  |
Total regulatory liabilities | 6,413,000,000 | 6,017,000,000
Less: current regulatory liabilities | (158,000,000) | (120,000,000)
Noncurrent regulatory liabilities | 6,255,000,000 | 5,897,000,000
Under-recovered FAC |  |
Regulatory assets: |  |
Total regulatory assets | 137,000,000 | 41,000,000
Under-recovered FAC | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 137,000,000 | 41,000,000
Under-recovered FAC | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 0
MTM derivative losses |  |
Regulatory assets: |  |
Total regulatory assets | 126,000,000 | 103,000,000
MTM derivative losses | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 15,000,000 | 15,000,000
MTM derivative losses | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 111,000,000 | 88,000,000
IEIMA revenue requirement reconciliation adjustment |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 139,000,000
IEIMA revenue requirement reconciliation adjustment | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 0
IEIMA revenue requirement reconciliation adjustment | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | $ 0 | 139,000,000
Regulatory liabilities: |  |
Regulatory asset, amortization period | 2 years |
MYRP revenue requirement reconciliation adjustment |  |
Regulatory assets: |  |
Total regulatory assets | $ 74,000,000 | 24,000,000
MYRP revenue requirement reconciliation adjustment | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 0
MYRP revenue requirement reconciliation adjustment | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 74,000,000 | 24,000,000
Under-recovered RBA |  |
Regulatory assets: |  |
Total regulatory assets | 29,000,000 | 22,000,000
Under-recovered RBA | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 0
Under-recovered RBA | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 29,000,000 | 22,000,000
FERC revenue requirement reconciliation adjustment |  |
Regulatory assets: |  |
Total regulatory assets | $ 73,000,000 | 90,000,000
Regulatory liabilities: |  |
Regulatory asset, amortization period | 2 years |
FERC revenue requirement reconciliation adjustment | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | $ 0 | 0
FERC revenue requirement reconciliation adjustment | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 45,000,000 | 55,000,000
Under-recovered VBA |  |
Regulatory assets: |  |
Total regulatory assets | 21,000,000 | 49,000,000
Under-recovered VBA | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 0
Under-recovered VBA | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 21,000,000 | 49,000,000
Income taxes |  |
Regulatory assets: |  |
Total regulatory assets | 376,000,000 | 322,000,000
Regulatory liabilities: |  |
Total regulatory liabilities | $ 1,587,000,000 | 1,804,000,000
Weighted-average amortization period | 38 years |
Income taxes | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | $ 282,000,000 | 237,000,000
Regulatory liabilities: |  |
Total regulatory liabilities | $ 963,000,000 | 1,040,000,000
Regulatory asset, amortization period | 5 years |
Weighted-average amortization period | 30 years |
Income taxes | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | $ 91,000,000 | 81,000,000
Regulatory liabilities: |  |
Total regulatory liabilities | $ 546,000,000 | 679,000,000
Weighted-average amortization period | 44 years |
Bad debt rider |  |
Regulatory assets: |  |
Total regulatory assets | $ 13,000,000 | 25,000,000
Bad debt rider | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 0
Bad debt rider | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 13,000,000 | 25,000,000
Callaway refueling and maintenance outage costs |  |
Regulatory assets: |  |
Total regulatory assets | 32,000,000 | 13,000,000
Callaway refueling and maintenance outage costs | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | $ 32,000,000 | 13,000,000
Regulatory liabilities: |  |
Regulatory asset, amortization period | 18 months |
Callaway refueling and maintenance outage costs | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | $ 0 | 0
Unamortized loss on reacquired debt |  |
Regulatory assets: |  |
Total regulatory assets | 44,000,000 | 47,000,000
Unamortized loss on reacquired debt | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 40,000,000 | 42,000,000
Unamortized loss on reacquired debt | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 4,000,000 | 5,000,000
Environmental cost riders |  |
Regulatory assets: |  |
Total regulatory assets | 46,000,000 | 43,000,000
Environmental cost riders | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 0
Environmental cost riders | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 46,000,000 | 43,000,000
Storm costs |  |
Regulatory assets: |  |
Total regulatory assets | 15,000,000 | 18,000,000
Storm costs | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 0
Storm costs | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 15,000,000 | 18,000,000
Customer generation rebate program |  |
Regulatory assets: |  |
Total regulatory assets | 141,000,000 | 89,000,000
Customer generation rebate program | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 0
Customer generation rebate program | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 141,000,000 | 89,000,000
PISA |  |
Regulatory assets: |  |
Total regulatory assets | 558,000,000 | 464,000,000
PISA | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | $ 558,000,000 | 464,000,000
Regulatory liabilities: |  |
Regulatory asset, amortization period | 20 years |
PISA | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | $ 0 | 0
Rush Island Energy Center securitization |  |
Regulatory assets: |  |
Total regulatory assets | 443,000,000 | 465,000,000
Rush Island Energy Center securitization | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 443,000,000 | 465,000,000
Rush Island Energy Center securitization | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 0
RESRAM |  |
Regulatory assets: |  |
Total regulatory assets | 44,000,000 | 51,000,000
RESRAM | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 44,000,000 | 51,000,000
RESRAM | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 0
Certain Meramec Energy Center costs |  |
Regulatory assets: |  |
Total regulatory assets | 14,000,000 | 26,000,000
Certain Meramec Energy Center costs | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | $ 14,000,000 | 26,000,000
Regulatory liabilities: |  |
Regulatory asset, amortization period | 5 years |
Certain Meramec Energy Center costs | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | $ 0 | 0
FEJA energy-efficiency rider |  |
Regulatory assets: |  |
Total regulatory assets | 624,000,000 | 576,000,000
FEJA energy-efficiency rider | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 0 | 0
FEJA energy-efficiency rider | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 624,000,000 | 576,000,000
Property Tax Tracker |  |
Regulatory assets: |  |
Total regulatory assets | 18,000,000 | 22,000,000
Property Tax Tracker | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | $ 18,000,000 | 22,000,000
Property Tax Tracker | Ameren Missouri | Electric |  |
Regulatory liabilities: |  |
Regulatory asset, amortization period | 3 years |
Property Tax Tracker | Ameren Missouri | Natural gas |  |
Regulatory liabilities: |  |
Regulatory asset, amortization period | 5 years |
Property Tax Tracker | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | $ 0 | 0
Other regulatory assets |  |
Regulatory assets: |  |
Total regulatory assets | 83,000,000 | 134,000,000
Other regulatory assets | Ameren Missouri |  |
Regulatory assets: |  |
Total regulatory assets | 48,000,000 | 56,000,000
Other regulatory assets | Ameren Illinois |  |
Regulatory assets: |  |
Total regulatory assets | 34,000,000 | 78,000,000
Over-recovered Illinois electric power costs |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 85,000,000 | 34,000,000
Over-recovered Illinois electric power costs | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 0 | 0
Over-recovered Illinois electric power costs | Ameren Illinois |  |
Regulatory liabilities: |  |
Total regulatory liabilities | $ 85,000,000 | 34,000,000
Amortization period | 1 year |
Over-recovered PGA |  |
Regulatory liabilities: |  |
Total regulatory liabilities | $ 42,000,000 | 35,000,000
Over-recovered PGA | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 3,000,000 | 2,000,000
Over-recovered PGA | Ameren Illinois |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 39,000,000 | 33,000,000
MTM derivative gains |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 16,000,000 | 16,000,000
MTM derivative gains | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 12,000,000 | 10,000,000
MTM derivative gains | Ameren Illinois |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 4,000,000 | 6,000,000
Cost of removal |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 2,511,000,000 | 2,294,000,000
Cost of removal | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 1,203,000,000 | 1,118,000,000
Cost of removal | Ameren Illinois |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 1,230,000,000 | 1,115,000,000
AROs |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 841,000,000 | 691,000,000
AROs | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 841,000,000 | 691,000,000
AROs | Ameren Illinois |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 0 | 0
Pension and postretirement benefit costs |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 467,000,000 | 358,000,000
Pension and postretirement benefit costs | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 230,000,000 | 202,000,000
Pension and postretirement benefit costs | Ameren Illinois |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 237,000,000 | 156,000,000
Pension and postretirement benefit costs tracker |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 9,000,000 | 70,000,000
Pension and postretirement benefit costs tracker | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | $ 9,000,000 | 70,000,000
Regulatory liability, amortization period | 4 years |
Pension and postretirement benefit costs tracker | Ameren Illinois |  |
Regulatory liabilities: |  |
Total regulatory liabilities | $ 0 | 0
Renewable energy credits and zero emission credits |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 699,000,000 | 586,000,000
Renewable energy credits and zero emission credits | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 0 | 0
Renewable energy credits and zero emission credits | Ameren Illinois |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 699,000,000 | 586,000,000
Certain Rush Island Energy Center Costs |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 31,000,000 | 66,000,000
Certain Rush Island Energy Center Costs | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 31,000,000 | 66,000,000
Certain Rush Island Energy Center Costs | Ameren Illinois |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 0 | 0
Rush Island Energy Center base rate revenue deferral |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 31,000,000 | 13,000,000
Rush Island Energy Center base rate revenue deferral | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | $ 31,000,000 | 13,000,000
Regulatory liability, amortization period | 3 years |
Rush Island Energy Center base rate revenue deferral | Ameren Illinois |  |
Regulatory liabilities: |  |
Total regulatory liabilities | $ 0 | 0
Other regulatory liabilities |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 94,000,000 | 50,000,000
Other regulatory liabilities | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | 24,000,000 | 1,000,000
Other regulatory liabilities | Ameren Illinois |  |
Regulatory liabilities: |  |
Total regulatory liabilities | $ 67,000,000 | 43,000,000
FAC adjustments | Ameren Missouri |  |
Regulatory liabilities: |  |
Accumulation period | 4 months |
Regulatory asset, amortization period | 8 months |
Asset Retirement Obligation - Nuclear decommissioning trust fund balance | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | $ 1,526,000,000 | 1,342,000,000
Asset Retirement Obligation - removal costs | Ameren Missouri |  |
Regulatory liabilities: |  |
Total regulatory liabilities | $ 685,000,000 | $ 651,000,000
Minimum | FEJA energy-efficiency rider | Ameren Illinois |  |
Regulatory liabilities: |  |
Regulatory asset, amortization period | 1 year |
Maximum | FEJA energy-efficiency rider | Ameren Illinois |  |
Regulatory liabilities: |  |
Regulatory asset, amortization period | 13 years |

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