Commitments And Contingencies (Schedule Of Estimated Purchased Power Commitments) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended
	Feb. 29, 2012 MWH	Dec. 31, 2011
Note payable issued for investment		$ 17
2012		1,972	[1]
2013		1,516	[1]
2014		1,211	[1]
2015		999	[1]
2016		930	[1]
Thereafter		2,486	[1]
Total		9,114	[1]
Megawatthours of energy products purchased in rate stability procuement	13,000,000
Price per megawatthour of energy products purchased in rate stability procurement	31
Coal [Member]
2012		1,120	[1]
2013		792	[1]
2014		692	[1]
2015		687	[1]
2016		674	[1]
Thereafter		968	[1]
Total		4,933	[1]
Natural Gas [Member]
2012		398	[1]
2013		295	[1]
2014		220	[1]
2015		116	[1]
2016		39	[1]
Thereafter		134	[1]
Total		1,202	[1]
Nuclear Fuel [Member]
2012		36	[1]
2013		37	[1]
2014		96	[1]
2015		90	[1]
2016		100	[1]
Thereafter		298	[1]
Total		657	[1]
Purchased Power [Member]
2012		196	[1]
2013		309	[1]
2014		125	[1]
2015		51	[1]
2016		52	[1]
Thereafter		746	[1]
Total		1,479	[1]
Methane Gas [Member]
2012		1	[1]
2013		3	[1]
2014		3	[1]
2015		3	[1]
2016		3	[1]
Thereafter		94	[1]
Total		107	[1]
Other [Member]
2012		221	[1]
2013		80	[1]
2014		75	[1]
2015		52	[1]
2016		62	[1]
Thereafter		246	[1]
Total		$ 736	[1]

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