Income Taxes (Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 453		$ 531
Tax credit carryforwards	$ 144		$ 131
Tax credit carryforward, expiration period start	Jan. 01, 2016		Jan. 01, 2013
Deferred Tax Assets, Charitable Contribution Carryforwards	$ 10	[1]	$ 19	[2]
Deferred Tax Assets, Valuation Allowance, Noncurrent	(4)	[3]	6	[4]
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent	6		13
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	407	[5]	457	[6]
Tax credit carryforwards	$ 105	[7]	$ 99	[8]
Net operating loss carryforward, expiration period start	Jan. 01, 2029		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	$ 46	[9]	$ 74	[10]
Tax credit carryforwards	41	[11]	36	[12]
Tax Credit Carryforward, Valuation Allowance	$ (2)	[3]	$ 4	[4]
Net operating loss carryforward, expiration period start	Jan. 01, 2023		Jan. 01, 2019
Tax credit carryforward, expiration period start	Jan. 01, 2016		Jan. 01, 2013
Union Electric Company
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 39		$ 86
Tax credit carryforwards	26		21
Union Electric Company | Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	35	[5]	75	[6]
Tax credit carryforwards	26	[7]	21	[8]
Union Electric Company | State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	4	[9]	11	[10]
Tax credit carryforwards	0	[11]	1	[12]
Tax Credit Carryforward, Valuation Allowance	0	[3]	(1)	[4]
Ameren Illinois Company
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	131		137
Tax credit carryforwards	2		2
Ameren Illinois Company | Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	127	[5]	127	[6]
Tax credit carryforwards	1	[7]	1	[8]
Ameren Illinois Company | State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	4	[9]	10	[10]
Tax credit carryforwards	1	[11]	2	[12]
Tax Credit Carryforward, Valuation Allowance	0	[3]	(1)	[4]
Other
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	283		308
Tax credit carryforwards	116		108
Deferred Tax Assets, Charitable Contribution Carryforwards	10	[1]	19	[2]
Deferred Tax Assets, Valuation Allowance, Noncurrent	(4)	[3]	(6)	[4]
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent	6		13
Other | Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	245	[5]	255	[6]
Tax credit carryforwards	78	[7]	77	[8]
Other | State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	38	[9]	53	[10]
Tax credit carryforwards	40	[11]	33	[12]
Tax Credit Carryforward, Valuation Allowance	$ (2)	[3]	$ (2)	[4]

[1] (f)Will begin to expire in 2016.

[2] (f)Began to expire in 2013.

[3] See Schedule II under Part IV, Item 15, in this report for information on changes in the valuation allowance.

[4] See Schedule II under Part IV, Item 15, in this report for information on changes in the valuation allowance.

[5] Will begin to expire in 2029.

[6] Will begin to expire in 2028

[7] Will begin to expire in 2029

[8] Will begin to expire in 2029

[9] Will begin to expire in 2023

[10] Will begin to expire in 2019

[11] Will begin to expire in 2016

[12] Began to expire in 2013