Selected Quarterly Information (Summary Of Selected Quarterly Information) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Selected Quarterly Financial Information [Line Items]
Operating revenues	$ 1,322,000,000	$ 1,638,000,000	$ 1,403,000,000	$ 1,475,000,000	$ 1,258,000,000	$ 1,709,000,000	$ 1,402,000,000	$ 1,412,000,000	$ 5,838,000,000	$ 5,781,000,000	$ 6,148,000,000
Operating Income	171,000,000	567,000,000	261,000,000	185,000,000	112,000,000	570,000,000	347,000,000	159,000,000	1,184,000,000	1,188,000,000	1,033,000,000
Net income (loss)	38,000,000	304,000,000	96,000,000	(143,000,000)	(1,155,000,000)	374,000,000	210,000,000	(403,000,000)	295,000,000	(974,000,000)	526,000,000
Net income attributable to Ameren Corporation - continuing operations	48,000,000	305,000,000	105,000,000	54,000,000	12,000,000	302,000,000	164,000,000	38,000,000	512,000,000	516,000,000	431,000,000
Net income (loss) attributable to Ameren Corporation - discontinued operations	(11,000,000)	(3,000,000)	(10,000,000)	(199,000,000)	(1,168,000,000)	72,000,000	47,000,000	(441,000,000)	223,000,000	1,490,000,000	(88,000,000)
Net income (loss) attributable to Ameren Corporation	37,000,000	302,000,000	95,000,000	(145,000,000)	(1,156,000,000)	374,000,000	211,000,000	(403,000,000)	289,000,000	(974,000,000)	519,000,000
Impairment and other charges
Earnings per common share - basic - continuing operations	$ 0.19	$ 1.26	$ 0.44	$ 0.22	$ 0.05	$ 1.25	$ 0.67	$ 0.16	$ 2.11	$ 2.13	$ 1.79
Earnings (loss) per common share - basic - discontinued operations	$ (0.04)	$ (0.01)	$ (0.05)	$ (0.82)	$ (4.81)	$ 0.29	$ 0.20	$ (1.82)	$ (0.92)	$ (6.14)	$ 0.36
Earnings (loss) per common share - basic	$ 0.15	$ 1.25	$ 0.39	$ (0.60)	$ (4.76)	$ 1.54	$ 0.87	$ (1.66)	$ 1.19	$ (4.01)	$ 2.15
Earnings per common share - diluted - continuing operations	$ 0.19	$ 1.25	$ 0.44	$ 0.22	$ 0.05	$ 1.25	$ 0.67	$ 0.16	$ 2.10	$ 2.13	$ 1.79
Earnings (loss) per common share - diluted - discontinued operations	$ (0.04)	$ (0.01)	$ (0.05)	$ (0.82)	$ (4.81)	$ 0.29	$ 0.20	$ (1.82)	$ (0.92)	$ (6.14)	$ 0.36
Earnings (loss) per common share - diluted	$ 0.15	$ 1.24	$ 0.39	$ (0.60)	$ (4.76)	$ 1.54	$ 0.87	$ (1.66)	$ 1.18	$ (4.01)	$ 2.15
Union Electric Company
Selected Quarterly Financial Information [Line Items]
Operating revenues	763,000,000	1,093,000,000	889,000,000	796,000,000	673,000,000	1,064,000,000	844,000,000	691,000,000	3,541,000,000	3,272,000,000	3,383,000,000
Operating Income	96,000,000	417,000,000	179,000,000	111,000,000	69,000,000	429,000,000	269,000,000	78,000,000	803,000,000	845,000,000	609,000,000
Net income (loss)									398,000,000	419,000,000	290,000,000
Net income (loss) attributable to Ameren Corporation	33,000,000	239,000,000	85,000,000	41,000,000	16,000,000	237,000,000	144,000,000	22,000,000	398,000,000	419,000,000	290,000,000
Net Income Available to Common Stockholder	33,000,000	238,000,000	84,000,000	40,000,000	16,000,000	236,000,000	143,000,000	21,000,000	395,000,000	416,000,000	287,000,000
Ameren Illinois Company
Selected Quarterly Financial Information [Line Items]
Operating revenues	564,000,000	547,000,000	516,000,000	684,000,000	589,000,000	648,000,000	564,000,000	724,000,000	2,311,000,000	2,525,000,000	2,787,000,000
Operating Income	85,000,000	158,000,000	87,000,000	85,000,000	51,000,000	151,000,000	86,000,000	89,000,000	415,000,000	377,000,000	458,000,000
Net income (loss)									163,000,000	144,000,000	196,000,000
Net income (loss) attributable to Ameren Corporation	22,000,000	77,000,000	32,000,000	32,000,000	12,000,000	71,000,000	33,000,000	28,000,000	163,000,000	144,000,000	196,000,000
Net Income Available to Common Stockholder	21,000,000	77,000,000	31,000,000	31,000,000	11,000,000	71,000,000	32,000,000	27,000,000	160,000,000	141,000,000	193,000,000
Merchant Generation
Selected Quarterly Financial Information [Line Items]
Impairment and other charges										$ 2,600,000,000