Income Taxes (Schedule Of Components Of Income Tax Expense (Benefit)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Income Taxes [Line Items]
Current Federal taxes	$ (118)	[1]	$ 40	[1]	$ (6)	[1]
Current State taxes	19	[1]	10	[1]	(2)	[1]
Deferred Federal taxes	368	[1]	204	[1]	213	[1]
Deferred State taxes	48	[1]	60	[1]	55	[1]
Deferred investment tax credits, amortization	(6)	[1]	(7)	[1]	(6)	[1]
Total income tax expense	311	[1]	307	[1]	254	[1]
Union Electric Company
Income Taxes [Line Items]
Current Federal taxes	136		(25)		3
Current State taxes	41		(10)		2
Deferred Federal taxes	64		248		129
Deferred State taxes	6		44		31
Deferred investment tax credits, amortization	(5)		(5)		(4)
Total income tax expense	242		252		161
Ameren Illinois Company
Income Taxes [Line Items]
Current Federal taxes	(15)		(7)		(24)
Current State taxes	21		(3)		(4)
Deferred Federal taxes	99		76		123
Deferred State taxes	6		30		34
Deferred investment tax credits, amortization	(1)		(2)		(2)
Total income tax expense	110		94		127
Other Affiliates [Member]
Income Taxes [Line Items]
Current Federal taxes	(239)	[2]	72		15
Current State taxes	(43)	[2]	23		0
Deferred Federal taxes	205	[2]	(120)		(39)
Deferred State taxes	36	[2]	(14)		(10)
Deferred investment tax credits, amortization	0		0		0
Total income tax expense	$ (41)		$ (39)		$ (34)

[1] Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.

[2] These amounts are substantially related to the reversal of unrecognized tax benefits as a result of new 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. They also reflect the increase in deferred tax expense due to available net operating losses.