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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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- Definition

Amount of asset (liability), recognized in statement of financial position, for defined benefit pension and other postretirement plans.

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