Summary Of Significant Accounting Policies (Schedule Of Asset Retirement Obligations) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance	$ 369,000,000		$ 349,000,000
Liabilities incurred	2,000,000
Liabilities settled	(2,000,000)		(1,000,000)
Accretion in period	21,000,000	[1]	19,000,000	[1]
Change in estimates	6,000,000	[2],[3]	2,000,000	[3]
Balance	396,000,000		369,000,000
Nuclear decommissioning trust fund	549,000,000		494,000,000
Union Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance	366,000,000		346,000,000
Liabilities incurred	2,000,000
Liabilities settled	(2,000,000)		(1,000,000)
Accretion in period	21,000,000	[1]	19,000,000	[1]
Change in estimates	2,000,000	[3]	2,000,000	[3]
Balance	389,000,000		366,000,000
Nuclear decommissioning trust fund	549,000,000		494,000,000
Ameren Illinois Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance	3,000,000	[4]	3,000,000
Liabilities settled	(1,000,000)	[5]	(1,000,000)	[5]
Accretion in period	1,000,000	[1],[5]	1,000,000	[1],[5]
Change in estimates	4,000,000	[1]	1,000,000	[5]
Balance	$ 7,000,000	[4]	$ 3,000,000	[4]

[1] (b)Accretion expense was recorded as an increase to regulatory assets at Ameren Missouri and Ameren Illinois.

[2] (e)Ameren Illinois changed its fair value estimate for asbestos removal in 2014.

[3] c)Ameren Missouri changed its fair value estimates for asbestos removal in 2013 and 2014 and for certain CCR facilities in 2013.

[4] (d)Included in “Other deferred credits and liabilities” on the balance sheet.

[5] (a)Less than $1 million.