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Retirement Benefits (Summary Of Benefit Liability Recorded) (Details) - USD ($) $ in Millions | Dec. 31, 2025 | Dec. 31, 2024
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Noncurrent asset | $ (954) | $ (734)
Ameren Missouri |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Noncurrent asset | (261) | (201)
Ameren Illinois |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Noncurrent asset | $ (563) | $ (438)

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