Income Taxes (Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 408	[1]	$ 200	[1]
Tax credit carryforwards	118	[1]	109	[1]
Change in valuation allowance	2		1
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	360	[1],[2]	173	[1],[3]
Tax credit carryforwards	88	[1],[4]	86	[1],[4]
Net operating loss carryforward, expiration period start	Jan. 01, 2028		Jan. 01, 2028
Tax credit carryforward, expiration period start	Jan. 01, 2029		Jan. 01, 2029
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	48	[1],[5]	27	[1],[6]
Tax credit carryforwards	34	[1],[7]	25	[1],[8]
Tax Credit Carryforward, Valuation Allowance	4	[1],[9]	2	[1],[10]
Net operating loss carryforward, expiration period start	Jan. 01, 2017		Jan. 01, 2017
Tax credit carryforward, expiration period start	Jan. 01, 2014		Jan. 01, 2013
Union Electric Company
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	64		64
Tax credit carryforwards	12		11
Union Electric Company | Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	61	[2]	61	[3]
Tax credit carryforwards	12	[4]	11	[4]
Union Electric Company | State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	3	[5]	3	[6]
Tax credit carryforwards	1	[7]	1	[8]
Tax Credit Carryforward, Valuation Allowance	(1)	[9]	(1)	[10]
Ameren Illinois Company
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	95		72
Tax credit carryforwards
Change in valuation allowance			1
Ameren Illinois Company | Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	84	[2]	61	[3]
Tax credit carryforwards			0	[4]
Ameren Illinois Company | State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	11	[5]	11	[6]
Tax credit carryforwards	1	[7]	1	[8]
Tax Credit Carryforward, Valuation Allowance	(1)	[9]	(1)	[10]
Other Affiliates [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	249		64
Tax credit carryforwards	106		98
Other Affiliates [Member] | Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	215	[2]	51	[3]
Tax credit carryforwards	76	[4]	75	[4]
Other Affiliates [Member] | State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	34	[5]	13	[6]
Tax credit carryforwards	32	[7]	23	[8]
Tax Credit Carryforward, Valuation Allowance	$ (2)	[9]	$ 0	[10]

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

[2] These will begin to expire in 2028.

[3] These will begin to expire in

[4] These will begin to expire in 2029.

[5] These will begin to expire in 2017.

[6] These will begin to expire in2017.

[7] These will begin to expire in 2014.

[8] These began to expire in 2013.

[9] This balance increased by $2 million, $- million and $- million for Ameren, Ameren Missouri and Ameren Illinois, respectively, during 2013.

[10] This balance increased by $1 million, $- million and $1 million for Ameren, Ameren Missouri and Ameren Illinois, respectively, during 2012.