Retirement Benefits (Components Of Net Periodic Benefit Cost) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Curtailment loss	$ (19)	[1],[2]
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	91	[1],[3]	81	[1],[3]	73	[1]
Interest cost	163	[1],[3]	166	[1],[3]	175	[1]
Expected return on plan assets	(218)	[1]	(208)	[1]	(211)	[1]
Transition obligation		[1]		[1]		[1]
Prior service cost	(2)	[1]	(3)	[1]	(1)	[1]
Actuarial loss	87	[1]	75	[1]	41	[1]
Curtailment loss	(12)	[1]
Net periodic benefit cost(b)	109	[1],[2]	111	[1],[4]	77	[1],[4]
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	22	[1],[3]	22	[1],[3]	20	[1]
Interest cost	46	[1],[3]	47	[1],[3]	54	[1]
Expected return on plan assets	(62)	[1]	(56)	[1]	(50)	[1]
Transition obligation		[1]	2	[1]	2	[1]
Prior service cost	(6)	[1]	(6)	[1]	(6)	[1]
Actuarial loss	8	[1]	5	[1]	3	[1]
Curtailment loss	(7)	[1]
Net periodic benefit cost(b)	1	[1],[2]	14	[1],[4]	23	[1],[4]
New Ameren Energy Resources Company, LLC | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost(b)	6	[1],[2]	9	[1],[2]	7	[1],[2]
New Ameren Energy Resources Company, LLC | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost(b)	$ 7	[1],[2]		[1],[2]		[1],[2]

[1] Includes amounts for Ameren registrant and nonregistrant subsidiaries

[2] (b)The net periodic benefit cost includes a $6 million and a $7 million net gain for pension benefits and postretirement benefits, respectively, which was included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). This net gain includes the curtailment gain recognized in 2013 as a result of a significant reduction in employees as of the December 2, 2013 closing date of the New AER divestiture. See Note 16 – Divestiture Transactions and Discontinued Operations for additional information on the divestiture.

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

[4] (c)The net periodic benefit cost includes $9 million and $- million in total net costs for pension benefits and postretirement benefits, respectively, for 2012 which were included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). The net periodic benefit cost includes $7 million and $- million in total net costs for pension benefits and postretirement benefits, respectively, for 2011 which were included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). See Note 16 – Divestiture Transactions and Discontinued Operations for additional information on the divestiture.