Other Income and Expenses (Other Income and Expenses) (Details) (USD $) In Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Miscellaneous income:
Allowance for equity funds used during construction	$ 9	[1]	$ 13	[1]	$ 15	[1]	$ 26	[1]
Interest income on industrial development revenue bonds	7	[1]	7	[1]	14	[1]	14	[1]
Interest and dividend income	1	[1]	1	[1]	2	[1]	2	[1]
Other			3	[1]	2	[1]	4	[1]
Total miscellaneous income	17	[1]	24	[1]	33	[1]	46	[1]
Miscellaneous expense:
Donations	1	[1]	1	[1]	3	[1]	3	[1]
Other	4	[1]	1	[1]	7	[1]	6	[1]
Total miscellaneous expense	$ 5	[1]	$ 2	[1]	$ 10	[1]	$ 9	[1]

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