Income Taxes (Schedule Of Deferred Tax Assets And Liabilities Resulting From Temporary Differences) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Income Taxes [Line Items]
Plant related	$ 4,185		$ 3,769
Regulatory assets, net	78		76
Deferred benefit costs	(220)		(273)
Revenue Requirement Reconciliation Adjustment	69
Revenue requirement reconciliation adjustments			(2)
ARO	(675)		(541)
Other	134		115
Total net accumulated deferred income tax liabilities	3,571	[1]	3,144	[2]
Current assets	352		106
Union Electric Company
Income Taxes [Line Items]
Plant related	2,776		2,513
Regulatory assets, net	82		74
Deferred benefit costs	(80)		(74)
ARO	(107)		(76)
Other	86		67
Total net accumulated deferred income tax liabilities	2,757	[1]	2,504	[2]
Current assets	49		20
Ameren Illinois Company
Income Taxes [Line Items]
Plant related	1,393		1,243
Regulatory assets, net			2
Regulatory assets, net	(5)
Deferred benefit costs	(45)		(85)
Revenue Requirement Reconciliation Adjustment	66
Revenue requirement reconciliation adjustments			(4)
ARO	(139)		(95)
Other			10
Deferred Tax Assets, Other	(22)
Total net accumulated deferred income tax liabilities	1,248	[1]	1,071	[2]
Current assets	160		45
Other
Income Taxes [Line Items]
Plant related	16		13
Regulatory assets, net	1
Deferred benefit costs	(95)		(114)
Revenue Requirement Reconciliation Adjustment	3		2
ARO	(429)		(370)
Other	70		38
Total net accumulated deferred income tax liabilities	$ (434)	[1]	$ (431)	[2]

[1] Includes $49 million recorded in "Other current assets" on Ameren Missouri's balance sheet as of December 31, 2014.

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