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Long-Term Debt And Equity Financings (Schedule Of Maturities Of Long-Term Debt) (Details) - USD ($) $ in Millions | Dec. 31, 2025 | Dec. 31, 2024 | Aug. 31, 2024
--- | --- | --- | ---
Debt Instrument [Line Items] |  |  |
2026 | $ 973 |  |
2027 | 974 |  |
2028 | 966 |  |
2029 | 1,207 |  |
2030 | 917 |  |
Thereafter | 14,394 |  |
Total | 19,431 |  |
Ameren (parent) |  |  |
Debt Instrument [Line Items] |  |  |
2026 | 950 |  |
2027 | 500 |  |
2028 | 450 |  |
2029 | 700 |  |
2030 | 0 |  |
Thereafter | 1,550 |  |
Total | 4,150 |  |
Unamortized discount, premium, and debt issuance costs | 19 |  |
Ameren Missouri |  |  |
Debt Instrument [Line Items] |  |  |
2026 | 23 |  |
2027 | 424 |  |
2028 | 26 |  |
2029 | 477 |  |
2030 | 493 |  |
Thereafter | 6,864 |  |
Total | 8,307 |  |
Unamortized discount, premium, and debt issuance costs | 77 |  |
Ameren Illinois |  |  |
Debt Instrument [Line Items] |  |  |
2026 | 0 |  |
2027 | 0 |  |
2028 | 490 |  |
2029 | 0 |  |
2030 | 375 |  |
Thereafter | 5,448 |  |
Total | 6,313 |  |
Unamortized discount, premium, and debt issuance costs | 54 |  |
Ameren Transmission Company of Illinois |  |  |
Debt Instrument [Line Items] |  |  |
2026 | 0 |  |
2027 | 50 |  |
2028 | 0 |  |
2029 | 30 |  |
2030 | 49 |  |
Thereafter | 532 |  |
Total | 661 |  |
Unamortized discount, premium, and debt issuance costs | 2 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 2.45% Senior unsecured notes due 2036 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 75 | $ 75 |
Long-term debt interest rate | 2.45% |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 2.45% Senior unsecured notes due 2036 | Debt Instrument, Redemption, Period One |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | $ 30 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 2.45% Senior unsecured notes due 2036 | Debt Instrument, Redemption, Period Two |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | 45 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 3.43% Senior unsecured notes due 2050 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 351 | 351 |
Long-term debt interest rate | 3.43% |  | 3.43%
Unsecured Debt | Ameren Transmission Company of Illinois | 3.43% Senior unsecured notes due 2050 | Debt Instrument, Redemption, Period Three |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | $ 50 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 3.43% Senior unsecured notes due 2050 | Debt Instrument, Redemption, Period Four |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | 49 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 3.43% Senior unsecured notes due 2050 | Debt Instrument, Redemption, Period Five |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | 50 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 3.43% Senior unsecured notes due 2050 | Debt Instrument, Redemption, Period Six |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | 49 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 3.43% Senior unsecured notes due 2050 | Debt Instrument, Redemption, Period Seven |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | 77 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 3.43% Senior unsecured notes due 2050 | Debt Instrument, Redemption, Period Eight |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | 76 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 2.96% Senior unsecured notes due 2052 |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument face amount | $ 95 | $ 95 |
Long-term debt interest rate | 2.96% |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 2.96% Senior unsecured notes due 2052 | Debt Instrument, Redemption, Period One |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | $ 45 |  |
Unsecured Debt | Ameren Transmission Company of Illinois | 2.96% Senior unsecured notes due 2052 | Debt Instrument, Redemption, Period Two |  |  |
Debt Instrument [Line Items] |  |  |
Thereafter | $ 50 |  |

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