Commitments And Contingencies (Schedule Of Estimated Purchased Power Commitments) (Details) (USD $) In Millions	Sep. 30, 2011
2011	$ 585	[1]
2012	1,953	[1]
2013	1,519	[1]
2014	1,243	[1]
2015	989	[1]
Thereafter	3,394	[1]
Total	9,683	[1]
Coal [Member]
2011	215	[1]
2012	1,134	[1]
2013	785	[1]
2014	698	[1]
2015	691	[1]
Thereafter	1,653	[1]
Total	5,176	[1]
Natural Gas [Member]
2011	121	[1]
2012	417	[1]
2013	304	[1]
2014	224	[1]
2015	118	[1]
Thereafter	186	[1]
Total	1,370	[1]
Nuclear Fuel [Member]
2011	50	[1]
2012	36	[1]
2013	38	[1]
2014	114	[1]
2015	74	[1]
Thereafter	397	[1]
Total	709	[1]
Purchased Power [Member]
2011	61	[1]
2012	196	[1]
2013	310	[1]
2014	125	[1]
2015	51	[1]
Thereafter	798	[1]
Total	1,541	[1]
Methane Gas [Member]
2012	1	[1]
2013	3	[1]
2014	3	[1]
2015	3	[1]
Thereafter	98	[1]
Total	108	[1]
Other [Member]
2011	138	[1]
2012	169	[1]
2013	79	[1]
2014	79	[1]
2015	52	[1]
Thereafter	262	[1]
Total	$ 779	[1]

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