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		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (47)	$ (54)	$ (64)	$ (21)
Included in regulatory assets/liabilities	(22)	(4)	(10)	(37)
Settlements, assets	1	0	6	0
Change in unrealized gains (losses) related to assets/liabilities held at period end	(20)	(4)	(8)	(25)
Ending balance	(68)	(58)	(68)	(58)
Union Electric Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	14	14	4	12
Included in regulatory assets/liabilities	(1)	(5)	13	3
Settlement, liabilities	(3)	(3)	(7)	(9)
Change in unrealized gains (losses) related to assets/liabilities held at period end	(1)	(5)	10	6
Ending balance	10	6	10	6
Ameren Illinois Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(61)	(68)	(68)	(33)
Included in regulatory assets/liabilities	(21)	1	(23)	(40)
Settlements, assets	4	3	13	9
Change in unrealized gains (losses) related to assets/liabilities held at period end	(19)	1	(18)	(31)
Ending balance	$ (78)	$ (64)	$ (78)	$ (64)