Income Taxes (Schedule Of Components Of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Current Federal taxes	$ (1)	$ (2)	$ (37)
Current State taxes	(3)	(4)	(37)
Deferred Federal taxes	299	299	369
Deferred State taxes	92	76	88
Deferred investment tax credits, amortization	(5)	(6)	(6)
Total income tax expense	382	363	377
Union Electric Company
Income Taxes [Line Items]
Current Federal taxes	31	110	(13)
Current State taxes	6	17	(3)
Deferred Federal taxes	161	71	222
Deferred State taxes	23	16	28
Deferred investment tax credits, amortization	(5)	(5)	(5)
Total income tax expense	216	209	229
Ameren Illinois Company
Income Taxes [Line Items]
Current Federal taxes	(8)	(83)	(51)
Current State taxes	12	(11)	(2)
Deferred Federal taxes	117	193	159
Deferred State taxes	37	29	38
Deferred investment tax credits, amortization	0	(1)	(1)
Total income tax expense	158	127	143
Other
Income Taxes [Line Items]
Current Federal taxes	(24)	(29)	27
Current State taxes	(21)	(10)	(32)
Deferred Federal taxes	21	35	(12)
Deferred State taxes	32	31	22
Deferred investment tax credits, amortization	0	0	0
Total income tax expense	$ 8	$ 27	$ 5