Commitments And Contingencies (Schedule Of Lease Obligations) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Commitments and Contingencies [Line Items]
Capital lease payments, 2014	$ 32	[1],[2]
Capital lease payments, 2015	33	[1],[2]
Capital lease payments, 2016	33	[1],[2]
Capital lease payments, 2017	33	[1],[2]
Capital lease payments, 2018	32	[1],[2]
Capital lease payments, After 5 Years	393	[1],[2]
Capital lease payments, Total	556	[1],[2]
Less Amount representing interest, 2014	27	[2]
Less Amount representing interest, 2015	27	[2]
Less Amount representing interest, 2016	27	[2]
Less Amount representing interest, 2017	27	[2]
Less Amount representing interest, 2018	26	[2]
Less Amount representing interest, After 5 Years	123	[2]
Less Amount representing interest, Total	257	[2]
Present value of minimum capital lease payments, 2014	5	[2]
Present value of minimum capital lease payments, 2015	6	[2]
Present value of minimum capital lease payments, 2016	6	[2]
Present value of minimum capital lease payments, 2017	6	[2]
Present value of minimum capital lease payments, 2018	6	[2]
Present value of minimum capital lease payments, After 5 Years	270	[2]
Present value of minimum capital lease payments, Total	299	[2]
Operating leases, 2014	14	[2],[3]
Operating leases, 2015	13	[2],[3]
Operating leases, 2016	13	[2],[3]
Operating leases, 2017	13	[2],[3]
Operating leases, 2018	13	[2],[3]
Operating leases, After 5 Years	51	[2],[3]
Operating leases, Total	117	[2],[3]
Total lease obligations, 2014	19	[2]
Total lease obligations, 2015	19	[2]
Total lease obligations, 2016	19	[2]
Total lease obligations, 2017	19	[2]
Total lease obligations, 2018	19	[2]
Total lease obligations, After 5 Years	321	[2]
Total lease obligations, Total	416	[2]
Annual obligation for real estate leases and railroad licenses	2
Total rental expense	32	[4]	33	[4]	36	[4]
Union Electric Company
Commitments and Contingencies [Line Items]
Capital lease payments, 2014	32	[1]
Capital lease payments, 2015	33	[1]
Capital lease payments, 2016	33	[1]
Capital lease payments, 2017	33	[1]
Capital lease payments, 2018	32	[1]
Capital lease payments, After 5 Years	393	[1]
Capital lease payments, Total	556	[1]
Less Amount representing interest, 2014	27
Less Amount representing interest, 2015	27
Less Amount representing interest, 2016	27
Less Amount representing interest, 2017	27
Less Amount representing interest, 2018	26
Less Amount representing interest, After 5 Years	123
Less Amount representing interest, Total	257
Present value of minimum capital lease payments, 2014	5
Present value of minimum capital lease payments, 2015	6
Present value of minimum capital lease payments, 2016	6
Present value of minimum capital lease payments, 2017	6
Present value of minimum capital lease payments, 2018	6
Present value of minimum capital lease payments, After 5 Years	270
Present value of minimum capital lease payments, Total	299
Operating leases, 2014	11	[3]
Operating leases, 2015	11	[3]
Operating leases, 2016	11	[3]
Operating leases, 2017	12	[3]
Operating leases, 2018	11	[3]
Operating leases, After 5 Years	50	[3]
Operating leases, Total	106	[3]
Total lease obligations, 2014	16
Total lease obligations, 2015	17
Total lease obligations, 2016	17
Total lease obligations, 2017	18
Total lease obligations, 2018	17
Total lease obligations, After 5 Years	320
Total lease obligations, Total	405
Annual obligation for real estate leases and railroad licenses	1
Total rental expense	29		29		29
Ameren Illinois Company
Commitments and Contingencies [Line Items]
Operating leases, 2014	2	[3]
Operating leases, 2015	1	[3]
Operating leases, 2016	1	[3]
Operating leases, 2017	1	[3]
Operating leases, 2018	1	[3]
Operating leases, After 5 Years	1	[3]
Operating leases, Total	7	[3]
Annual obligation for real estate leases and railroad licenses	1
Total rental expense	$ 21		$ 19		$ 17

[1] See Properties under Part I, Item 2, and Note 3 – Property and Plant, Net, of this report for additional information.

[2] ncludes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.

[3] Amounts related to certain land-related leases have indefinite payment periods. The annual obligation of $2 million, $1 million and $1 million for Ameren, Ameren Missouri and Ameren Illinois for these items is included in the 2014 through 2018 columns, respectively.

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