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Retirement Benefits (Summary Of Benefit Plan Costs Incurred) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | $ (148) | $ (4) | $ 62
Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (83) | (54) | (34)
Ameren Missouri | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (76) | (3) | 29
Ameren Missouri | Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (30) | (14) | (4)
Ameren Illinois | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (62) | 3 | 34
Ameren Illinois | Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (54) | (41) | (31)
Other | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (10) | (4) | (1)
Other | Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | $ 1 | $ 1 | $ 1

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