Income Taxes (Schedule Of Components Of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Current Federal taxes	$ (10)	$ 5	$ (1)
Current State taxes	23	32	(3)
Deferred Federal Income Tax Expense (Benefit)	220	511	299
Deferred State taxes	49	34	92
Amortization of Excess Deferred Taxes	(40)
Deferred investment tax credits, amortization	(5)	(6)	(5)
Total income tax expense	237	576	382
Union Electric Company
Income Taxes [Line Items]
Current Federal taxes	104	149	31
Current State taxes	29	23	6
Deferred Federal Income Tax Expense (Benefit)	22	76	161
Deferred State taxes	(2)	11	23
Amortization of Excess Deferred Taxes	(24)
Deferred investment tax credits, amortization	(5)	(5)	(5)
Total income tax expense	124	254	216
Ameren Illinois Company
Income Taxes [Line Items]
Current Federal taxes	4	(34)	(8)
Current State taxes	6	29	12
Deferred Federal Income Tax Expense (Benefit)	75	185	117
Deferred State taxes	28	(13)	37
Amortization of Excess Deferred Taxes	(15)
Deferred investment tax credits, amortization	0	(1)	0
Total income tax expense	98	166	158
Other
Income Taxes [Line Items]
Current Federal taxes	(118)	(110)	(24)
Current State taxes	(12)	(20)	(21)
Deferred Federal Income Tax Expense (Benefit)	123	250	21
Deferred State taxes	23	36	32
Amortization of Excess Deferred Taxes	(1)
Deferred investment tax credits, amortization	0	0	0
Total income tax expense	$ 15	$ 156	$ 8