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Retirement Benefits (Schedule Of Matching Contributions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 49	$ 49	$ 49
Ameren Missouri
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	26	26	27
Ameren Illinois
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	22	22	21
Other
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 1	$ 1	$ 1

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