Income Taxes (Schedule Of Components Of Income Tax Expense (Benefit)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Income Taxes [Line Items]
Current Federal taxes	$ (37)		$ (118)		$ 40
Current State taxes	(37)		19		10
Deferred Federal taxes	369		368		204
Deferred State taxes	88		48		60
Deferred investment tax credits, amortization	(6)		(6)		(7)
Total income tax expense	377		311		307
Union Electric Company
Income Taxes [Line Items]
Current Federal taxes	(13)		136		(25)
Current State taxes	(3)		41		(10)
Deferred Federal taxes	222		64		248
Deferred State taxes	28		6		44
Deferred investment tax credits, amortization	(5)		(5)		(5)
Total income tax expense	229		242		252
Ameren Illinois Company
Income Taxes [Line Items]
Current Federal taxes	(51)		(15)		(7)
Current State taxes	(2)		21		(3)
Deferred Federal taxes	159		99		76
Deferred State taxes	38		6		30
Deferred investment tax credits, amortization	(1)		(1)		(2)
Total income tax expense	143		110		94
Other
Income Taxes [Line Items]
Current Federal taxes	27	[1]	(239)	[1]	72
Current State taxes	(32)	[1]	(43)	[1]	23
Deferred Federal taxes	(12)	[1]	205	[1]	(120)
Deferred State taxes	22	[1]	36	[1]	(14)
Deferred investment tax credits, amortization	0		0		0
Total income tax expense	$ 5		$ (41)		$ (39)

[1] These amounts are substantially related to the reversal of unrecognized tax benefits as a result of IRS guidance related to the deductibility of expenditures to maintain, replace or improve steam or electric power generation property, along with casualty loss deductions for storm damage. The amounts also reflect the increase in deferred tax expense due to available net operating losses.