Other Income And Expenses (Other Income And Expenses) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	$ 37	[1]	$ 36	[1]	$ 34	[1]
Interest income on industrial development revenue bonds	27	[1]	28	[1]	28	[1]
Interest and dividend income	3	[1]	4	[1],[2]	3	[1]
Other	2	[1]	2	[1]	3	[1]
Total miscellaneous income	69	[1]	70	[1]	68	[1]
Donations	12	[1]	24	[1],[3]	8	[1]
Other	14	[1]	13	[1]	15	[1]
Total miscellaneous expense	26	[1]	37	[1]	23	[1]
Union Electric Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	31		31		30
Interest income on industrial development revenue bonds	27		28		28
Interest and dividend income			4	[2]	2
Other					1
Total miscellaneous income	58		63		61
Donations	4		9		3
Other	7		5		7
Total miscellaneous expense	11		14		10
Ameren Illinois Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	6		5		4
Interest and dividend income	2				1
Other	2		2		2
Total miscellaneous income	10		7		7
Donations	4		11	[3]	1
Other	5		6		5
Total miscellaneous expense	9		17		6
Illinois Science and Energy Innovation Trust | Ameren Illinois Company
Other Nonoperating Income (Expense) [Line Items]
One-time Donation	$ 7.5

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

[2] Includes interest income received in 2012 relating to a refund of charges included in an expired power purchase agreement with Entergy.

[3] Includes Ameren Illinois' one-time $7.5 million donation to the Illinois Science and Energy Innovation Trust pursuant to the IEIMA as a result of Ameren Illinois' 2012 participation in the electric delivery formula ratemaking process.