Consolidated Statement of Income (Loss) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Operating Revenues:
Electric	$ 1,143		$ 1,106
Gas	413		488
Total operating revenues	1,556		1,594
Operating Expenses:
Fuel	206		204
Purchased power	139		114
Gas purchased for resale	236		304
Other operations and maintenance	401		418
Depreciation and amortization	193		181
Taxes other than income taxes	125		127
Total operating expenses	1,300		1,348
Operating Income	256		246
Other Income and Expenses:
Miscellaneous income	19	[1]	18	[1]
Miscellaneous expense	11	[1]	9	[1]
Total other income (expense)	8		9
Interest Charges	88		92
Income Before Income Taxes	176		163
Income Taxes	66		64
Income from Continuing Operations	110		99
Loss from Discontinued Operations, Net of Taxes (Note 12)	0		(1)
Net Income (Loss)	110		98
Comprehensive Income	108		96
Less: Net Income (Loss) Attributable to Noncontrolling Interests:
Net Income from Continuing Operations Attributable to Noncontrolling Interests	2		2
Net Income (Loss):
Continuing Operations	108		97
Discontinued Operations	0		(1)
Net Income (Loss)	108		96
Earnings Per Share, Basic [Abstract]
Continuing Operations	$ 0.45		$ 0.40
Discontinued Operations	$ 0		$ 0
Earnings Per Share, Basic	$ 0.45		$ 0.40
Dividends per Common Share	$ 0.41		$ 0.40
Average Common Shares Outstanding - Basic	242.6		242.6
Union Electric Company
Operating Revenues:
Electric	742		749
Gas	58		68
Total operating revenues	800		817
Operating Expenses:
Fuel	206		204
Purchased power	39		35
Gas purchased for resale	31		40
Other operations and maintenance	211		225
Depreciation and amortization	118		116
Taxes other than income taxes	80		78
Total operating expenses	685		698
Operating Income	115		119
Other Income and Expenses:
Miscellaneous income	11		14
Miscellaneous expense	3		4
Total other income (expense)	8		10
Interest Charges	55		52
Income Before Income Taxes	68		77
Income Taxes	26		29
Net Income (Loss)	42		48
Other Comprehensive Income	0		0
Comprehensive Income	42		48
Net Income (Loss):
Net Income (Loss)	42		48
Earnings Per Share, Basic [Abstract]
Preferred Stock Dividends	1		1
Net Income Available to Common Stockholder	41		47
Ameren Illinois Company
Operating Revenues:
Electric	390		353
Gas	355		421
Total operating revenues	745		774
Operating Expenses:
Purchased power	102		81
Gas purchased for resale	205		264
Other operations and maintenance	202		200
Depreciation and amortization	73		63
Taxes other than income taxes	43		46
Total operating expenses	625		654
Operating Income	120		120
Other Income and Expenses:
Miscellaneous income	7		3
Miscellaneous expense	5		4
Total other income (expense)	2		(1)
Interest Charges	33		30
Income Before Income Taxes	89		89
Income Taxes	35		35
Net Income (Loss)	54		54
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	(1)		(1)
Comprehensive Income	53		53
Net Income (Loss):
Net Income (Loss)	54		54
Earnings Per Share, Basic [Abstract]
Preferred Stock Dividends	1		1
Net Income Available to Common Stockholder	$ 53		$ 53

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