Consolidated Statement Of Income (Loss) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Operating Revenues:
Electric	$ 1,310		$ 1,470
Gas	348		434
Total operating revenues	1,658		1,904
Operating Expenses:
Fuel	327		379
Purchased power	163		227
Gas purchased for resale	215		288
Other operations and maintenance	427		463
Asset impairment	628
Depreciation and amortization	199		195
Taxes other than income taxes	121		125
Total operating expenses	2,080		1,677
Operating Income (Loss)	(422)		227
Other Income and Expenses:
Miscellaneous income	17	[1]	16	[1]
Miscellaneous expense	15	[1]	5	[1]
Total other income (expense)	2		11
Interest Charges	113		119
Income (Loss) Before Income Taxes (Benefit)	(533)		119
Income Taxes (Benefit)	(130)		45
Net Income (Loss)	(403)		74
Less: Net Income Attributable to Noncontrolling Interests			3
Net Income(Loss)	(403)	[2]	71	[2]
Earnings (Loss) per Common Share - Basic and Diluted	$ (1.66)		$ 0.29
Dividends per Common Share	$ 0.40		$ 0.385
Average Common Shares Outstanding	242.6		240.6
Union Electric Company [Member]
Operating Revenues:
Electric	636		702
Gas	55		69
Other			1
Total operating revenues	691		772
Operating Expenses:
Fuel	180		229
Purchased power	20		20
Gas purchased for resale	32		40
Other operations and maintenance	202		233
Depreciation and amortization	108		100
Taxes other than income taxes	71		73
Total operating expenses	613		695
Operating Income (Loss)	78		77
Other Income and Expenses:
Miscellaneous income	15		13
Miscellaneous expense	3		3
Total other income (expense)	12		10
Interest Charges	56		54
Income (Loss) Before Income Taxes (Benefit)	34		33
Income Taxes (Benefit)	12		11
Net Income (Loss)	22		22
Preferred Stock Dividends	1		1
Net Income Available to Common Stockholder	21		21
Ameren Illinois Company [Member]
Operating Revenues:
Electric	431		442
Gas	293		366
Total operating revenues	724		808
Operating Expenses:
Purchased power	190		211
Gas purchased for resale	183		248
Other operations and maintenance	168		168
Depreciation and amortization	55		52
Taxes other than income taxes	39		41
Total operating expenses	635		720
Operating Income (Loss)	89		88
Other Income and Expenses:
Miscellaneous income	1		2
Miscellaneous expense	11		1
Total other income (expense)	(10)		1
Interest Charges	33		35
Income (Loss) Before Income Taxes (Benefit)	46		54
Income Taxes (Benefit)	18		20
Net Income (Loss)	28		34
Preferred Stock Dividends	1		1
Net Income Available to Common Stockholder	27		33
Ameren Energy Generating Company [Member]
Operating Revenues:
Total operating revenues	194		241
Operating Expenses:
Fuel	105		111
Other operations and maintenance	47		45
Depreciation and amortization	23		24
Taxes other than income taxes	6		7
Total operating expenses	181		187
Operating Income (Loss)	13		54
Other Income and Expenses:
Interest Charges	14		17
Income (Loss) Before Income Taxes (Benefit)	(1)		37
Income Taxes (Benefit)	2		15
Net Income (Loss)	(3)		22
Less: Net Income Attributable to Noncontrolling Interests	(2)		1
Net Income(Loss)	$ (1)		$ 21

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

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