Retirement Benefits (Funded Status Of Benefit Plans And Amounts Included In Regulatory Assets And OCI) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Change in plan assets:
Funded status – deficiency	$ (461)	[1]	$ (1,143)	[1]
Amounts recognized in the balance sheet consist of:
Noncurrent liability	466		1,138
Net liability recognized	461	[1]	1,143	[1]
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation at end of year	3,698	[1]	3,829	[1]
Change in benefit obligation:
Net benefit obligation at beginning of year	4,051	[1]	3,764	[1]
Service cost	91	[1],[2]	81	[1],[2]	73	[2]
Interest cost	163	[1],[2]	166	[1],[2]	175	[2]
Participant contributions		[1]		[1]
Actuarial (gain) loss	(207)	[1]	240	[1]
Curtailment gain(c)		[2],[3]		[2],[3]
Settlement		[1],[4]		[5]
Benefits paid	(198)	[1]	(200)	[1]
Net benefit obligation at end of year	3,900	[1]	4,051	[1]	3,764	[1]
Change in plan assets:
Fair value of plan assets at beginning of year	3,127	[1]	2,814	[1]
Actual return on plan assets	376	[1]	385	[1]
Employer contributions	156	[1]	128	[1]	96	[1]
Participant contributions		[1]		[1]
Benefits paid	(198)	[1]	(200)	[1]
Fair value of plan assets at end of year	3,461	[1]	3,127	[1]	2,814	[1]
Funded status – deficiency	439	[1]	924	[1]
Accrued benefit cost at December 31	439	[1]	924	[1]
Amounts recognized in the balance sheet consist of:
Noncurrent asset
Current liability(f)	3	[1],[6]	3	[1],[6]
Noncurrent liability	436	[1]	921	[1]
Net liability recognized	439	[1]	924	[1]
Amounts recognized in regulatory assets consist of:
Net actuarial (gain) loss	282	[1]	699	[1]
Prior service cost (credit)	(7)	[1]	(6)	[1]
Amounts (pretax) recognized in accumulated OCI consist of:
Net actuarial (gain) loss	17	[1]	65	[1]
Prior service cost (credit)		[1]	(14)	[1]
Total	292	[1]	744	[1]
Postretirement Benefits
Change in benefit obligation:
Net benefit obligation at beginning of year	1,157	[1]	1,145	[1]
Service cost	22	[1],[2]	22	[1],[2]	20	[2]
Interest cost	46	[1],[2]	47	[1],[2]	54	[2]
Participant contributions	16	[1]	16	[1]
Actuarial (gain) loss	(76)	[1]	(10)	[1]
Curtailment gain(c)	(3)	[2],[3]		[2],[3]
Settlement	5	[1],[4]		[5]
Benefits paid	(64)	[1]	(69)	[1]
Early retiree reinsurance program receipt		[1]	2	[1]
Federal subsidy on benefits paid	3	[1]	4	[1]
Net benefit obligation at end of year	1,096	[1]	1,157	[1]	1,145	[1]
Change in plan assets:
Fair value of plan assets at beginning of year	938	[1]	836	[1]
Actual return on plan assets	156	[1]	104	[1]
Employer contributions	25	[1]	45	[1]	129	[1]
Federal subsidy on benefits paid	3	[1]	4	[1]
Early retiree reinsurance program receipt		[1]	2	[1]
Participant contributions	16	[1]	16	[1]
Benefits paid	(64)	[1]	(69)	[1]
Fair value of plan assets at end of year	1,074	[1]	938	[1]	836	[1]
Funded status – deficiency	22	[1]	219	[1]
Accrued benefit cost at December 31	22	[1]	219	[1]
Amounts recognized in the balance sheet consist of:
Noncurrent asset	9	[1],[7]
Current liability(f)	1	[1],[6]	2	[1],[6]
Noncurrent liability	30	[1]	217	[1]
Net liability recognized	22	[1]	219	[1]
Amounts recognized in regulatory assets consist of:
Net actuarial (gain) loss	(71)	[1]	103	[1]
Prior service cost (credit)	(20)	[1]	(24)	[1]
Amounts (pretax) recognized in accumulated OCI consist of:
Net actuarial (gain) loss	(12)	[1]	5	[1]
Prior service cost (credit)	(1)	[1]	(6)	[1]
Total	$ (104)	[1]	$ 78	[1]

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

[2] Includes amounts for Ameren registrant and nonregistrant subsidiaries

[3] Effective with the divestiture of New AER on December 2, 2013, the liability for active management employees of New AER and its subsidiaries not eligible to retire were neither transferred to IPH nor retained by Ameren, which resulted in a curtailment gain. See Note 16 – Divestiture Transactions and Discontinued Operations for further information on the divestiture.

[4] Effective with the divestiture of New AER on December 2, 2013, the liability for active union employees of New AER and its subsidiaries not eligible to retire was transferred to IPH based on the assumption of the collective bargaining agreements in place, which resulted in a settlement. See Note 16 – Divestiture Transactions and Discontinued Operations for further information on the divestiture.

[5] Not applicable.

[6] Included in "Other current liabilities" on Ameren's consolidated balance sheet.

[7] Included in "Other assets" on Ameren's consolidated balance sheet.