Consolidated Statement of Income (Loss) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Operating Revenues:
Electric	$ 1,228		$ 1,255		$ 2,316		$ 2,319
Gas	175		147		562		495
Total operating revenues	1,403		1,402		2,878		2,814
Operating Expenses:
Fuel	213		175		426		356
Purchased power	121		161		272		370
Gas purchased for resale	72		49		302		264
Other operations and maintenance	447		395		846		764
Depreciation and amortization	178		168		353		335
Taxes other than income taxes	111		110		233		223
Total operating expenses	1,142		1,058		2,432		2,312
Operating Income	261		344		446		502
Other Income and Expenses:
Miscellaneous income	16	[1]	19	[1]	31	[1]	36	[1]
Miscellaneous expense	5	[1]	7	[1]	13	[1]	22	[1]
Total other income (expense)	11		12		18		14
Interest Charges	100		98		201		196
Income Before Income Taxes	172		258		263		320
Income Taxes	66		96		101		119
Income from Continuing Operations	106		162		162		201
Income (Loss) from Discontinued Operations, Net of Taxes (Note 2)	(10)		48		(209)		(394)
Net Income (Loss)	96		210		(47)		(193)
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	10		1		10		1
Comprehensive Income (Loss)	101		216		(51)		(172)
Less: Net Income (Loss) Attributable to Noncontrolling Interests:
Continuing Operations	1		1		3		3
Discontinued Operations			(2)				(4)
Net Income (Loss):
Continuing Operations	105		161		159		198
Discontinued Operations	(10)		50		(209)		(390)
Net Income (Loss)	95		211		(50)		(192)
Earnings (Loss) per Common Share – Basic and Diluted:
Continuing Operations (in dollars per share)	$ 0.44		$ 0.66		$ 0.66		$ 0.81
Discontinued Operations (in dollars per share)	$ (0.05)		$ 0.21		$ (0.87)		$ (1.60)
Net Income (Loss) per Common Share - Basic and Diluted	$ 0.39		$ 0.87		$ (0.21)		$ (0.79)
Dividends per Common Share	$ 0.40		$ 0.40		$ 0.80		$ 0.80
Average Common Shares Outstanding	242.6		242.6		242.6		242.6
Union Electric Company [Member]
Operating Revenues:
Electric	860		822		1,592		1,458
Gas	29		21		93		76
Other			1.0				1.0
Total operating revenues	889		844		1,685		1,535
Operating Expenses:
Fuel	213		177		426		357
Purchased power	41				67		20
Gas purchased for resale	11		5		48		37
Other operations and maintenance	253		206		474		408
Depreciation and amortization	113		109		224		217
Taxes other than income taxes	79		78		156		149
Total operating expenses	710		575		1,395		1,188
Operating Income	179		269		290		347
Other Income and Expenses:
Miscellaneous income	14		18		28		33
Miscellaneous expense	3		4		8		7
Total other income (expense)	11		14		20		26
Interest Charges	56		56		116		112
Income Before Income Taxes	134		227		194		261
Income Taxes	49		83		68		95
Net Income (Loss)	85		144		126		166
Other Comprehensive Income	0		0		0		0
Comprehensive Income (Loss)	85		144		126		166
Net Income (Loss):
Net Income (Loss)	85		144		126		166
Earnings (Loss) per Common Share – Basic and Diluted:
Preferred Stock Dividends	1		1		2		2
Net Income Available to Common Stockholder	84		143		124		164
Ameren Illinois Company [Member]
Operating Revenues:
Electric	368		437		728		868
Gas	146		127		470		420
Other	2.0				2.0
Total operating revenues	516		564		1,200		1,288
Operating Expenses:
Purchased power	80		162		207		352
Gas purchased for resale	61		44		254		227
Other operations and maintenance	196		186		372		354
Depreciation and amortization	62		55		123		110
Taxes other than income taxes	30		31		72		70
Total operating expenses	429		478		1,028		1,113
Operating Income	87		86		172		175
Other Income and Expenses:
Miscellaneous income	2		2		3		3
Miscellaneous expense	1		2		4		13
Total other income (expense)	1				(1)		(10)
Interest Charges	34		31		65		64
Income Before Income Taxes	54		55		106		101
Income Taxes	22		22		42		40
Net Income (Loss)	32		33		64		61
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	(1)		(1)		(2)		(2)
Comprehensive Income (Loss)	31		32		62		59
Net Income (Loss):
Net Income (Loss)	32		33		64		61
Earnings (Loss) per Common Share – Basic and Diluted:
Preferred Stock Dividends	1		1		2		2
Net Income Available to Common Stockholder	$ 31		$ 32		$ 62		$ 59

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