Summary Of Significant Accounting Policies (Schedule Of Asset Retirement Obligations) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance	$ 349	[1]	$ 331	[1]
Liabilities incurred	0	[1]		[1]
Liabilities settled	(1)	[1]	(1)	[1]
Accretion in period	19	[1],[2]	18	[1],[2]
Change in estimates	2	[1],[3]	1	[1],[3]
Balance	369	[1]	349	[1]
Nuclear decommissioning trust fund	494		408
Union Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance	346	[1]	328	[1]
Liabilities incurred		[1]		[1]
Liabilities settled	(1)	[1]	(1)	[1]
Accretion in period	19	[1],[2]	18	[1],[2]
Change in estimates	2	[1],[3]	1	[1],[3]
Balance	366	[1]	346	[1]
Nuclear decommissioning trust fund	494		408
Ameren Illinois Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance	3	[4]	3	[4]
Liabilities incurred		[4]		[4]
Liabilities settled	1	[4],[5]	1	[4],[5]
Accretion in period	1	[2],[4],[5]	1	[2],[4],[5]
Change in estimates	1	[4],[5]	1	[4],[5]
Balance	$ 3	[4]	$ 3	[4]

[1] The nuclear decommissioning trust fund assets of $494 million and $408 million as of December 31, 2013, and 2012, respectively, are restricted for decommissioning of the Callaway energy center.

[2] Accretion expense was recorded as an increase to regulatory assets at Ameren Missouri and Ameren Illinois.

[3] Ameren Missouri changed its fair value estimates for asbestos removal in 2012 and 2013, and for certain CCR storage facilities in 2013.

[4] Balance included in “Other deferred credits and liabilities” on the balance sheet.

[5] Less than $1 million.