Consolidated Statement Of Income (Loss) (USD $) In Millions, except Per Share data	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Operating Revenues:
Electric	$ 2,138		$ 2,133		$ 5,222		$ 5,140
Gas	130		134		731		792
Total operating revenues	2,268		2,267		5,953		5,932
Operating Expenses:
Fuel	467		394		1,217		973
Purchased power	332		376		796		915
Gas purchased for resale	46		51		413		467
Other operations and maintenance	432		455		1,368		1,357
Goodwill, impairment and other charges	124		589		126		589
Depreciation and amortization	196		194		585		571
Taxes other than income taxes	121		119		355		342
Total operating expenses	1,718		2,178		4,860		5,214
Operating Income	550		89		1,093		718
Other Income and Expenses:
Miscellaneous income	18	[1]	24	[1]	51	[1]	70	[1]
Miscellaneous expense	5	[1]	10	[1]	15	[1]	19	[1]
Total other income	13		14		36		51
Interest Charges	113		130		336		377
Income (Loss) Before Income Taxes	450		(27)		793		392
Income Taxes	163		137		293		295
Net Income (Loss)	287	[1]	(164)	[1]	500	[1]	97	[1]
Less: Net Income Attributable to Noncontrolling Interests	2	[1]	3	[1]	6	[1]	10	[1]
Net Income (Loss) Attributable to Ameren Corporation	285	[2]	(167)	[2]	494	[2]	87	[2]
Earnings (Loss) per Common Share - Basic and Diluted	$ 1.18		$ (0.70)		$ 2.05		$ 0.37
Dividends per Common Share	$ 0.385		$ 0.385		$ 1.155		$ 1.155
Average Common Shares Outstanding	241.7		239.3		241.2		238.4
Union Electric Company [Member]
Operating Revenues:
Electric	1,099		1,040		2,592		2,384
Gas	16		20		113		118
Other					4		1
Total operating revenues	1,115		1,060		2,709		2,503
Operating Expenses:
Fuel	249		205		682		441
Purchased power	35		48		81		134
Gas purchased for resale	4		8		55		64
Other operations and maintenance	218		233		682		691
Loss from regulatory disallowance	89				89
Depreciation and amortization	102		99		300		283
Taxes other than income taxes	85		82		234		218
Total operating expenses	782		675		2,123		1,831
Operating Income	333		385		586		672
Other Income and Expenses:
Miscellaneous income	16		23		45		64
Miscellaneous expense	2		8		8		11
Total other income	14		15		37		53
Interest Charges	54		56		153		158
Income (Loss) Before Income Taxes	293		344		470		567
Income Taxes	102		120		166		200
Net Income (Loss)	191		224		304		367
Preferred Stock Dividends	1		1		3		4
Net Income Available to Common Stockholder	190		223		301		363
Ameren Illinois Company [Member]
Operating Revenues:
Electric	631		632	[3]	1,556		1,630	[3]
Gas	114		114	[3]	619		674	[3]
Other					1
Total operating revenues	745		746	[3]	2,176		2,304	[3]
Operating Expenses:
Purchased power	270		286	[3]	677		782	[3]
Gas purchased for resale	43		42	[3]	358		401	[3]
Other operations and maintenance	152		155	[3]	501		476	[3]
Depreciation and amortization	55		52	[3]	161		158	[3]
Taxes other than income taxes	29		29	[3]	96		95	[3]
Total operating expenses	549		564	[3]	1,793		1,912	[3]
Operating Income	196		182	[3]	383		392	[3]
Other Income and Expenses:
Miscellaneous income	2		2	[3]	5		6	[3]
Miscellaneous expense	2		2	[3]	4		6	[3]
Total other income					1
Interest Charges	33		37	[3]	103		108	[3]
Income (Loss) Before Income Taxes	163		145	[3]	281		284	[3]
Income Taxes	65		54	[3]	111		109	[3]
Income from Continuing Operations	98		91	[3]	170		175	[3]
Income from Discontinued Operations, net of tax			19	[3]			40	[3]
Net Income (Loss)	98		110	[3]	170		215	[3]
Preferred Stock Dividends			1	[3]	2		4	[3]
Net Income Available to Common Stockholder	98		109	[3]	168		211	[3]
Ameren Energy Generating Company [Member]
Operating Revenues:
Total operating revenues	327		335		828		877
Operating Expenses:
Fuel	169		146		410		405
Purchased power	37		42		55		62
Other operations and maintenance	48		47		137		141
Goodwill, impairment and other charges	35		170		36		170
Depreciation and amortization	24		25		73		74
Taxes other than income taxes	4		4		16		17
Total operating expenses	317		434		727		869
Operating Income	10		(99)		101		8
Other Income and Expenses:
Miscellaneous income	1				1		1
Miscellaneous expense							1
Total other income	1				1
Interest Charges	16		21		47		60
Income (Loss) Before Income Taxes	(5)		(120)		55		(52)
Income Taxes	(1)		(20)		24		10
Net Income (Loss)	(4)		(100)		31		(62)
Less: Net Income Attributable to Noncontrolling Interests	1		1		2		3
Net Income (Loss) Attributable to Ameren Corporation	$ (5)		$ (101)		$ 29		$ (65)

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

[2] Represents net income (loss) available to common stockholders.

[3] Prior period reflects the Ameren Illinois Merger as discussed in Note 1 - Summary of Significant Accounting Policies.