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Retirement Benefits (Schedule Of Matching Contributions) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions | $ 49 | $ 43 | $ 38
Ameren Missouri |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions | 27 | 23 | 21
Ameren Illinois |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions | 21 | 19 | 16
Other |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions | $ 1 | $ 1 | $ 1

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