Schedule I - Condensed Financial Information Of Parent (Statement of Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Operating revenues	$ 1,322	$ 1,638	$ 1,403	$ 1,475	$ 1,258	$ 1,709	$ 1,402	$ 1,412	$ 5,838		$ 5,781		$ 6,148
Operating expenses									4,654		4,593		5,115
Operating Income	171	567	261	185	112	570	347	159	1,184		1,188		1,033
Interest income from affiliates									3	[1]	4	[1],[2]	3	[1]
Miscellaneous expense									26	[1]	37	[1]	23	[1]
Interest charges									398		392		387
Income taxes (benefit)									311	[1]	307	[1]	254	[1]
Net income attributable to Ameren Corporation - continuing operations	48	305	105	54	12	302	164	38	512		516		431
Net Income (Loss) Attributable to Ameren Corporation - Discontinued Operations	11	3	10	199	1,168	(72)	(47)	441	(223)		(1,490)		88
Net income (loss) attributable to Ameren Corporation	37	302	95	(145)	(1,156)	374	211	(403)	289		(974)		519
Comprehensive Income from Continuing Operations
Pension and other postretirement activity, net of income taxes (benefit)									30		(8)		(19)
Comprehensive Income (Loss) from Continuing Operations, Net of Tax, Portion Attributable to Parent									542		508		412
Other Comprehensive Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest									(18)		58		(20)
Comprehensive Income (Loss) from Discontinued Operations									(242)		(1,440)		74
Comprehensive Income (Loss) Attributable to Ameren Corporation									300		(932)		486
Other Comprehensive Income (Loss), Taxes:
Pension and other postretirement activity, tax (benefit)									16		(6)		(14)
Parent Company
Condensed Financial Statements, Captions [Line Items]
Operating revenues
Operating expenses									26		17		13
Operating Income									(26)		(17)		(13)
Equity in earnings of subsidiaries									546		546		464
Interest income from affiliates									3		3		5
Miscellaneous expense									5		4		4
Interest charges									42		39		41
Income taxes (benefit)									(36)		(27)		(20)
Net income attributable to Ameren Corporation - continuing operations									512		516		431
Net Income (Loss) Attributable to Ameren Corporation - Discontinued Operations									(223)		(1,490)		88
Net income (loss) attributable to Ameren Corporation									289		(974)		519
Comprehensive Income from Continuing Operations
Pension and other postretirement activity, net of income taxes (benefit)									30		(8)		(19)
Comprehensive Income (Loss) from Continuing Operations, Net of Tax, Portion Attributable to Parent									542		508		412
Other Comprehensive Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest									(19)		50		(14)
Comprehensive Income (Loss) from Discontinued Operations									(242)		(1,440)		74
Comprehensive Income (Loss) Attributable to Ameren Corporation									300		(932)		486
Other Comprehensive Income (Loss), Taxes:
Pension and other postretirement activity, tax (benefit)									$ 16		$ (6)		$ (14)

[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.