Property And Plant, Net (Accrued Capital Expenditures) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Property And Plant, Net [Abstract]
Accrued capital expenditures	$ 107	[1]	$ 79	[1]	$ 143	[1]

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