Income Taxes (Schedule Of Components Of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Current Federal taxes	$ (4)	$ (10)	$ 5
Current State taxes	19	23	32
Deferred Federal Income Tax Expense (Benefit)	185	220	511
Deferred State taxes	59	49	34
Amortization of Excess Deferred Taxes	(72)	(40)
Deferred investment tax credits, amortization	(5)	(5)	(6)
Total income tax expense	182	237	576
Union Electric Company
Income Taxes [Line Items]
Current Federal taxes	65	104	149
Current State taxes	22	29	23
Deferred Federal Income Tax Expense (Benefit)	37	22	76
Deferred State taxes	5	(2)	11
Amortization of Excess Deferred Taxes	(56)	(24)
Deferred investment tax credits, amortization	(5)	(5)	(5)
Total income tax expense	68	124	254
Ameren Illinois Company
Income Taxes [Line Items]
Current Federal taxes	19	4	(34)
Current State taxes	11	6	29
Deferred Federal Income Tax Expense (Benefit)	66	75	185
Deferred State taxes	29	28	(13)
Amortization of Excess Deferred Taxes	(15)	(15)
Deferred investment tax credits, amortization	0	0	(1)
Total income tax expense	110	98	166
Other
Income Taxes [Line Items]
Current Federal taxes	(88)	(118)	(110)
Current State taxes	(14)	(12)	(20)
Deferred Federal Income Tax Expense (Benefit)	82	123	250
Deferred State taxes	25	23	36
Amortization of Excess Deferred Taxes	(1)	(1)
Deferred investment tax credits, amortization	0	0	0
Total income tax expense	$ 4	$ 15	$ 156