Consolidated Statement of Income (Loss) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Operating Revenues:
Electric	$ 1,523		$ 1,507		$ 3,864		$ 3,823
Gas	147		131		819		693
Total operating revenues	1,670		1,638		4,683		4,516
Operating Expenses:
Fuel	236		222		638		648
Purchased power	112		128		335		400
Gas purchased for resale	49		42		432		344
Other operations and maintenance	404		383		1,236		1,229
Depreciation and amortization	187		175		551		528
Taxes other than income taxes	121		121		362		354
Total operating expenses	1,109		1,071		3,554		3,503
Operating Income	561		567		1,129		1,013
Other Income and Expenses:
Miscellaneous income	21	[1]	20	[1]	60	[1]	51	[1]
Miscellaneous expense	7	[1]	5	[1]	20	[1]	18	[1]
Total other income (expense)	14		15		40		33
Interest Charges	85		88		266		289
Income Before Income Taxes	490		494		903		757
Income Taxes	194		187		357		288
Income from Continuing Operations	296		307		546		469
Loss from Discontinued Operations, Net of Taxes (Note 12)	(1)		(3)		(3)		(212)
Net Income (Loss)	295		304		543		257
Pension and other postretirement benefit plan activity, net of income taxes (benefit)			(5)		3		5
Comprehensive Income	293		292		541		241
Less: Net Income (Loss) Attributable to Noncontrolling Interests:
Net Income from Continuing Operations Attributable to Noncontrolling Interests	2		2		5		5
Net Income (Loss):
Continuing Operations	294		305		541		464
Discontinued Operations	(1)		(3)		(3)		(212)
Net Income (Loss)	293		302		538		252
Earnings Per Share, Basic [Abstract]
Continuing Operations	$ 1.21		$ 1.26		$ 2.23		$ 1.92
Discontinued Operations			$ (0.01)		$ (0.01)		$ (0.88)
Earnings Per Share, Basic	$ 1.21		$ 1.25		$ 2.22		$ 1.04
Earnings Per Share, Diluted [Abstract]
Continuing Operations	$ 1.20		$ 1.25		$ 2.21		$ 1.91
Discontinued Operations			$ (0.01)		$ (0.01)		$ (0.88)
Earnings Per Share, Diluted	$ 1.20		$ 1.24		$ 2.20		$ 1.03
Dividends per Common Share	$ 0.40		$ 0.40		$ 1.20		$ 1.20
Average Common Shares Outstanding - Basic	242.6		242.6		242.6		242.6
Average Common Shares Outstanding - Diluted	244.3		245.1		244.3		244.4
Union Electric Company
Operating Revenues:
Electric	1,076		1,075		2,696		2,667
Gas	21		17		117		110
Other			1		1		1
Total operating revenues	1,097		1,093		2,814		2,778
Operating Expenses:
Fuel	236		222		638		648
Purchased power	25		33		86		100
Gas purchased for resale	7		4		58		52
Other operations and maintenance	228		212		677		686
Depreciation and amortization	118		114		351		338
Taxes other than income taxes	89		91		248		247
Total operating expenses	703		676		2,058		2,071
Operating Income	394		417		756		707
Other Income and Expenses:
Miscellaneous income	15		16		45		44
Miscellaneous expense	4		2		10		10
Total other income (expense)	11		14		35		34
Interest Charges	53		43		159		159
Income Before Income Taxes	352		388		632		582
Income Taxes	129		149		234		217
Net Income (Loss)	223		239		398		365
Other Comprehensive Income	0		0		0		0
Comprehensive Income	223		239		398		365
Net Income (Loss):
Net Income (Loss)	223		239		398		365
Earnings Per Share, Diluted [Abstract]
Preferred Stock Dividends	1		1		3		3
Net Income Available to Common Stockholder	222		238		395		362
Ameren Illinois Company
Operating Revenues:
Electric	445		432		1,162		1,160
Gas	127		115		703		585
Other							2
Total operating revenues	572		547		1,865		1,747
Operating Expenses:
Purchased power	89		96		256		303
Gas purchased for resale	43		38		374		292
Other operations and maintenance	185		166		580		538
Depreciation and amortization	66		59		193		182
Taxes other than income taxes	31		30		109		102
Total operating expenses	414		389		1,512		1,417
Operating Income	158		158		353		330
Other Income and Expenses:
Miscellaneous income	4		4		12		7
Miscellaneous expense	2		3		7		7
Total other income (expense)	2		1		5		0
Interest Charges	31		31		90		96
Income Before Income Taxes	129		128		268		234
Income Taxes	54		51		110		93
Net Income (Loss)	75		77		158		141
Pension and other postretirement benefit plan activity, net of income taxes (benefit)					(2)		(2)
Comprehensive Income	75		77		156		139
Net Income (Loss):
Net Income (Loss)	75		77		158		141
Earnings Per Share, Diluted [Abstract]
Preferred Stock Dividends					2		2
Net Income Available to Common Stockholder	$ 75		$ 77		$ 156		$ 139

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