Consolidated Statement Of Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net income	$ 526	$ 151	$ 624
Unrealized net gain (loss) on derivative hedging instruments, net of income taxes (benefit)	3	(2)	103
Reclassification adjustments for derivative (gains) losses included in net income, net of income taxes (benefit)	4	(8)	(112)
Reclassification adjustment due to implementation of FAC, net of income taxes			(29)
Pension and other postretirement activity, net of income taxes (benefit)	(46)	4	22
Total comprehensive income, net of taxes	487	145	608
Comprehensive income attributable to noncontrolling interests	1	10	14
Total comprehensive income (loss) attributable to Ameren Corporation, net of taxes	486	135	594
Union Electric Company [Member]
Net income	290	369	265
Unrealized net gain (loss) on derivative hedging instruments, net of income taxes (benefit)			17
Reclassification adjustments for derivative (gains) losses included in net income, net of income taxes (benefit)			(13)
Reclassification adjustment due to implementation of FAC, net of income taxes			(29)
Total comprehensive income, net of taxes	290	369	240
Ameren Illinois Company [Member]
Net income	196	252	247	[1],[2]
Pension and other postretirement activity, net of income taxes (benefit)	(3)	(4)	(4)	[2]
Other comprehensive income from discontinued operations		(1)	6	[2]
Total comprehensive income, net of taxes	193	247	249	[2]
Ameren Energy Generating Company [Member]
Net income	45	(36)	162	[3]
Reclassification adjustments for derivative (gains) losses included in net income, net of income taxes (benefit)	1
Pension and other postretirement activity, net of income taxes (benefit)	(34)	3	21	[3]
Total comprehensive income, net of taxes	12	(33)	183	[3]
Comprehensive income attributable to noncontrolling interests	(4)	2	4	[3]
Total comprehensive income (loss) attributable to Ameren Corporation, net of taxes	$ 16	$ (35)	$ 179	[3]

[1] Prior period has been adjusted to reflect the Ameren Illinois Merger as discussed in Note 1 - Summary of Significant Accounting Policies.

[2] Prior period has been adjusted to reflect the AIC Merger as discussed in Note 1 - Summary of Significant Accounting Policies.

[3] Prior period has been adjusted to include EEI as discussed in Note 1 - Summary of Significant Accounting Policies.