Commitments And Contingencies (Schedule Of Estimated Purchased Power Commitments) (Details) (USD $) In Millions, unless otherwise specified									12 Months Ended
	Dec. 31, 2013		Dec. 31, 2013 Coal		Dec. 31, 2013 Natural Gas		Dec. 31, 2013 Nuclear Fuel		Dec. 31, 2013 Purchased Power		Dec. 31, 2013 Methane Gas		Dec. 31, 2013 Other		Dec. 31, 2013 Union Electric Company	Dec. 31, 2013 Union Electric Company Coal	Dec. 31, 2013 Union Electric Company Natural Gas	Dec. 31, 2013 Union Electric Company Nuclear Fuel	Dec. 31, 2013 Union Electric Company Purchased Power		Dec. 31, 2013 Union Electric Company Methane Gas	Dec. 31, 2013 Union Electric Company Other	Dec. 31, 2013 Ameren Illinois Company	Dec. 31, 2013 Ameren Illinois Company Coal	Dec. 31, 2013 Ameren Illinois Company Natural Gas	Dec. 31, 2013 Ameren Illinois Company Nuclear Fuel	Dec. 31, 2013 Ameren Illinois Company Purchased Power		Dec. 31, 2013 Ameren Illinois Company Methane Gas	Dec. 31, 2013 Ameren Illinois Company Other	Dec. 31, 2015 Investment in Energy Efficiency Programs Union Electric Company	Dec. 31, 2014 Investment in Energy Efficiency Programs Union Electric Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2014	$ 1,519	[1]	$ 620	[1]	$ 323	[1]	$ 64	[1]	$ 308	[1],[2]	$ 3	[1]	$ 201	[1]	$ 895	$ 620	$ 62	$ 64	$ 19	[2]	$ 3	$ 127	$ 573		$ 261		$ 289	[2]		$ 23		$ 48
2015	1,195	[1]	642	[1]	179	[1]	63	[1]	164	[1],[2]	4	[1]	143	[1]	861	642	32	63	19	[2]	4	101	316		147		145	[2]		24	64
2016	993	[1]	664	[1]	90	[1]	81	[1]	78	[1],[2]	4	[1]	76	[1]	827	664	19	81	19	[2]	4	40	154		71		59	[2]		24
2017	888	[1]	676	[1]	45	[1]	58	[1]	55	[1],[2]	4	[1]	50	[1]	794	676	11	58	19	[2]	4	26	94		34		36	[2]		24
2018	313	[1]	120	[1]	28	[1]	57	[1]	52	[1],[2]	5	[1]	51	[1]	236	120	8	57	19	[2]	5	27	77		20		33	[2]		24
Thereafter	1,441	[1]	125	[1]	82	[1]	158	[1]	635	[1],[2]	91	[1]	350	[1]	695	125	28	158	110	[2]	91	183	746		54		525	[2]		167
Total	$ 6,349	[1]	$ 2,847	[1]	$ 747	[1]	$ 481	[1]	$ 1,292	[1],[2]	$ 111	[1]	$ 871	[1]	$ 4,308	$ 2,847	$ 160	$ 481	$ 205	[2]	$ 111	$ 504	$ 1,960		$ 587		$ 1,087	[2]		$ 286
Renewable Energy Credits Agreements, Term									20 years

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

[2] The purchased power amounts for Ameren and Ameren Illinois include 20-year agreements for renewable energy credits that were entered into in December 2010 with various renewable energy suppliers. The agreements contain a provision that allows Ameren Illinois to reduce the quantity purchased in the event that Ameren Illinois would not be able to recover the costs associated with the renewable energy credits.