Other Income And Expenses (Other Income And Expenses) (Details) (USD $) In Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Other Income And Expenses [Abstract]
Allowance for equity funds used during construction	$ 10	[1]	$ 14	[1]	$ 25	[1]	$ 40	[1]
Interest income on industrial development revenue bonds	7	[1]	7	[1]	21	[1]	21	[1]
Interest and dividend income	1	[1]	2	[1]	3	[1]	4	[1]
Other			1	[1]	2	[1]	5	[1]
Total miscellaneous income	18	[1]	24	[1]	51	[1]	70	[1]
Donations	1	[1]	7	[1]	4	[1]	10	[1]
Other	4	[1]	3	[1]	11	[1]	9	[1]
Total miscellaneous expense	$ 5	[1]	$ 10	[1]	$ 15	[1]	$ 19	[1]

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