Consolidated Statement of Income (Loss) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Operating Revenues:
Electric	$ 1,088		$ 1,064
Gas	387		348
Operating Revenues	1,475		1,412
Operating Expenses:
Fuel	213		181
Purchased power	151		209
Gas purchased for resale	230		215
Other operations and maintenance	399		369
Depreciation and amortization	175		167
Taxes other than income taxes	122		113
Total operating expenses	1,290		1,254
Operating Income	185		158
Other Income and Expenses:
Miscellaneous income	15	[1]	17	[1]
Miscellaneous expense	8	[1]	15	[1]
Total other income (expense)	7		2
Interest Charges	101		98
Income (Loss) Before Income Taxes	91		62
Income Taxes	35		23
Income from Continuing Operations	56		39
Loss from Discontinued Operations, Net of Taxes (Note 2)	(199)		(442)
Net Loss	(143)		(403)
Comprehensive Income (Loss)	(152)		(388)
Less: Net Income (Loss) Attributable to Noncontrolling Interests:
Continuing Operations	2		2
Discontinued Operations			(2)
Net Income (Loss):
Continuing Operations	54		37
Discontinued Operations	(199)		(440)
Net Income (Loss)	(145)		(403)
Earnings (Loss) per Common Share – Basic and Diluted:
Continuing Operations (in dollars per share)	$ 0.22		$ 0.15
Discontinued Operations (in dollars per share)	$ (0.82)		$ (1.81)
Earnings per Common Share - Basic and Diluted	$ (0.60)		$ (1.66)
Dividends per Common Share	$ 0.40		$ 0.40
Average Common Shares Outstanding	242.6		242.6
Union Electric Company [Member]
Operating Revenues:
Electric	732		636
Gas	64		55
Operating Revenues	796		691
Operating Expenses:
Fuel	213		180
Purchased power	26		20
Gas purchased for resale	37		32
Other operations and maintenance	221		202
Depreciation and amortization	111		108
Taxes other than income taxes	77		71
Total operating expenses	685		613
Operating Income	111		78
Other Income and Expenses:
Miscellaneous income	14		15
Miscellaneous expense	5		3
Total other income (expense)	9		12
Interest Charges	60		56
Income (Loss) Before Income Taxes	60		34
Income Taxes	19		12
Net Loss	41		22
Other Comprehensive Income	0		0
Comprehensive Income (Loss)	41		22
Net Income (Loss):
Net Income (Loss)	41		22
Earnings (Loss) per Common Share – Basic and Diluted:
Preferred Stock Dividends	1		1
Net Income Available to Common Stockholder	40		21
Ameren Illinois Company [Member]
Operating Revenues:
Electric	360		431
Gas	324		293
Operating Revenues	684		724
Operating Expenses:
Purchased power	127		190
Gas purchased for resale	193		183
Other operations and maintenance	176		168
Depreciation and amortization	61		55
Taxes other than income taxes	42		39
Total operating expenses	599		635
Operating Income	85		89
Other Income and Expenses:
Miscellaneous income	1		1
Miscellaneous expense	3		11
Total other income (expense)	(2)		(10)
Interest Charges	31		33
Income (Loss) Before Income Taxes	52		46
Income Taxes	20		18
Net Loss	32		28
Pension and other postretirement benefit plan activity, net of income taxes	(1)		(1)
Comprehensive Income (Loss)	31		27
Net Income (Loss):
Net Income (Loss)	32		28
Earnings (Loss) per Common Share – Basic and Diluted:
Preferred Stock Dividends	1		1
Net Income Available to Common Stockholder	$ 31		$ 27

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