Income Taxes (Schedule Of Deferred Tax Assets And Liabilities Resulting From Temporary Differences) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Income Taxes [Line Items]
Plant related	$ 3,769	[1]	$ 3,550	[1]
Regulatory assets (liabilities), net	76	[1]	73	[1]
Deferred benefit costs	(273)	[1]	(323)	[1]
Purchase accounting	(28)	[1]	(28)	[1]
ARO	(6)	[1]	(6)	[1]
Other	(478)	[1],[2],[3]	(250)	[1],[2]
Total net accumulated deferred income tax liabilities	3,060	[1],[4]	3,016	[1],[5]
Deferred Tax Assets, Valuation Allowance	7
Current assets	106		170
Union Electric Company
Income Taxes [Line Items]
Plant related	2,513		2,385
Regulatory assets (liabilities), net	74		73
Deferred benefit costs	(74)		(84)
Purchase accounting
ARO	(7)		(7)
Other	(17)	[2]	50	[2]
Total net accumulated deferred income tax liabilities	2,489	[4]	2,417	[5]
Deferred Tax Assets, Valuation Allowance	1
Current assets	20		26
Ameren Illinois Company
Income Taxes [Line Items]
Plant related	1,243		1,145
Regulatory assets (liabilities), net	2
Deferred benefit costs	(85)		(102)
Purchase accounting	(27)		(27)
ARO	1		1
Other	(63)	[2]	(77)	[2]
Total net accumulated deferred income tax liabilities	1,071	[4]	940	[5]
Deferred Tax Assets, Valuation Allowance	1
Current assets	45		85
Other Affiliates [Member]
Income Taxes [Line Items]
Plant related	13		20
Regulatory assets (liabilities), net
Deferred benefit costs	(114)		(137)
Purchase accounting	(1)		(1)
ARO	0		0
Other	(398)	[2]	(223)	[2]
Total net accumulated deferred income tax liabilities	$ (500)	[4]	$ (341)	[5]

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

[2] Includes deferred tax assets related to net operating loss and tax credit carryforwards detailed in the table below.

[3] Includes total valuation allowances for Ameren, Ameren Missouri, and Ameren Illinois of $7 million, $1 million, and $1 million, respectively, as of December 31, 2013. The state valuation allowances are shown in the table below.

[4] Includes $20 million recorded in "Other current assets" on Ameren Missouri's balance sheet as of December 31, 2013.

[5] Includes $26 million recorded in "Other current assets" on Ameren Missouri's balance sheet as of December 31, 2012.