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Retirement Benefits (Cash Contributions Made To Benefit Plans) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Cash contributions to benefit plans | $ 8 | $ 4 | $ 5
Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Cash contributions to benefit plans | 4 | 3 | 2
Ameren Missouri | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Cash contributions to benefit plans | 1 | 1 | 1
Ameren Missouri | Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Cash contributions to benefit plans | 2 | 2 | 1
Ameren Illinois | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Cash contributions to benefit plans | 1 | 2 | 3
Ameren Illinois | Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Cash contributions to benefit plans | 1 | 1 | 1
Other | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Cash contributions to benefit plans | 6 | 1 | 1
Other | Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Cash contributions to benefit plans | $ 1 | $ 0 | $ 0

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