Income Taxes (Schedule Of Components Of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Current Federal taxes	$ 7	$ 2	$ (4)
Current State taxes	(6)	5	19
Deferred Federal Income Tax Expense (Benefit)	170	187	185
Deferred State taxes	86	57	59
Amortization of excess deferred income taxes	(96)	(91)	(72)
Amortization of deferred investment tax credits	(4)	(5)	(5)
Income tax benefit	157	155	182
Union Electric Company
Income Taxes [Line Items]
Current Federal taxes	0	14	65
Current State taxes	0	3	22
Deferred Federal Income Tax Expense (Benefit)	65	82	37
Deferred State taxes	23	15	5
Amortization of excess deferred income taxes	(81)	(75)	(56)
Amortization of deferred investment tax credits	(4)	(5)	(5)
Income tax benefit	3	34	68
Ameren Illinois Company
Income Taxes [Line Items]
Current Federal taxes	(15)	12	19
Current State taxes	(7)	(6)	11
Deferred Federal Income Tax Expense (Benefit)	120	81	66
Deferred State taxes	59	52	29
Amortization of excess deferred income taxes	(14)	(15)	(15)
Amortization of deferred investment tax credits	0	0	0
Income tax benefit	143	124	110
Other
Income Taxes [Line Items]
Current Federal taxes	22	(24)	(88)
Current State taxes	1	8	(14)
Deferred Federal Income Tax Expense (Benefit)	(15)	24	82
Deferred State taxes	4	(10)	25
Amortization of excess deferred income taxes	(1)	(1)	(1)
Amortization of deferred investment tax credits	0	0	0
Income tax benefit	$ 11	$ (3)	$ 4