Fair Value Measurements (Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level Three In The Fair Value Hierarchy) (Details) - Power - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (47)	$ (64)
Included in regulatory assets/liabilities	(14)	9
Settlements, assets		(3)
Settlement, liabilities	1
Change in unrealized gains (losses) related to assets/liabilities held at period end	(14)	11
Ending balance	(62)	(52)
Union Electric Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	6	4
Included in regulatory assets/liabilities	2	(1)
Settlement, liabilities	(3)	(1)
Change in unrealized gains (losses) related to assets/liabilities held at period end	2	0
Ending balance	5	2
Ameren Illinois Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(53)	(68)
Included in regulatory assets/liabilities	(16)	10
Settlements, assets	2	4
Change in unrealized gains (losses) related to assets/liabilities held at period end	(16)	11
Ending balance	$ (67)	$ (54)