Compensation and Benefit Plans (Plan Assets and Benefit Obligation) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2008
Pension Plans
Pension and Other Postretirement Benefits
Expected contribution by employer in the next fiscal year	$ 20.0
Percentage of decline in market value of investments held in trust (as a percent)					35.00%
Change in projected benefit obligation
Projected benefit obligation at beginning of year	316		287
Service cost	16		16
Interest cost	14		14
Actuarial (gain) / loss	27		12
Curtailment (gain)/loss			0
Transfers out	(23)	[1]	0	[1]
Benefits paid	(11)		(13)
Projected benefit obligation at end of year	330		316
Change in plan assets
Fair value of plan assets at beginning of period	177		164
Actual return on plan assets	26		2
Employer contributions	23		24
Benefits paid	(11)		(13)
Fair value of plan assets at end of period	215		177
Funded status at end of year	(115)		(139)
Amounts recognized in the consolidated balance sheets:
Long-term liabilities	(115)		(139)
Amounts recognized in accumulated other comprehensive income:
Prior service cost (credit)	1		1
Net loss	67		69
Accumulated benefit obligation at end of year	300		278
Pension plans with an accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	330		316
Accumulated benefit obligation	300		278
Fair value of plan assets	216		177
Weighted-average assumptions used to determine obligations at end of year:
Discount rate	4.50%		4.50%
Rate of compensation increase	4.50%		4.50%
Pension Plans | Midwest Generation LLC
Pension and Other Postretirement Benefits
Expected contribution by employer in the next fiscal year	16.5
Change in projected benefit obligation
Projected benefit obligation at beginning of year	195		164
Service cost	14		13
Interest cost	8		8
Actuarial (gain) / loss	13		13
Curtailment (gain)/loss	0		0
Transfers out	0	[1]	0	[1]
Benefits paid	(5)		(3)
Projected benefit obligation at end of year	225		195
Change in plan assets
Fair value of plan assets at beginning of period	121		109
Actual return on plan assets	19		2
Employer contributions	14		13
Benefits paid	(5)		(3)
Fair value of plan assets at end of period	149		121
Funded status at end of year	(76)		(74)
Amounts recognized in the consolidated balance sheets:
Long-term liabilities	(76)		(74)
Amounts recognized in accumulated other comprehensive income:
Prior service cost (credit)	1		1
Net loss	40		38
Accumulated benefit obligation at end of year	195		168
Pension plans with an accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	225		195
Accumulated benefit obligation	195		168
Fair value of plan assets	148		121
Weighted-average assumptions used to determine obligations at end of year:
Discount rate	4.50%		4.50%
Rate of compensation increase	4.50%		4.50%
Pension Plans | Other EME Subsidiaries
Change in projected benefit obligation
Projected benefit obligation at beginning of year	121	[2]	123	[2]
Service cost	2	[2]	3	[2]
Interest cost	6	[2]	6	[2]
Actuarial (gain) / loss	14	[2]	(1)	[2]
Curtailment (gain)/loss	(9)	[2]	0	[2]
Transfers out	(23)	[1],[2]	0	[1],[2]
Benefits paid	(6)	[2]	(10)	[2]
Projected benefit obligation at end of year	105	[2]	121	[2]
Change in plan assets
Fair value of plan assets at beginning of period	56	[2]	55	[2]
Actual return on plan assets	7	[2]	0	[2]
Employer contributions	9	[2]	11	[2]
Benefits paid	(6)	[2]	(10)	[2]
Fair value of plan assets at end of period	66	[2]	56	[2]
Funded status at end of year	(39)	[2]	(65)	[2]
Amounts recognized in the consolidated balance sheets:
Long-term liabilities	(39)	[2]	(65)	[2]
Amounts recognized in accumulated other comprehensive income:
Prior service cost (credit)	0	[2]	0	[2]
Net loss	27	[2]	31	[2]
Accumulated benefit obligation at end of year	105	[2]	110	[2]
Pension plans with an accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	105	[2]	121	[2]
Accumulated benefit obligation	105	[2]	110	[2]
Fair value of plan assets	68	[2]	56	[2]
Weighted-average assumptions used to determine obligations at end of year:
Discount rate	4.50%	[2]	4.50%	[2]
Rate of compensation increase	4.50%	[2]	4.50%	[2]
Postretirement Benefits Other Than Pensions
Pension and Other Postretirement Benefits
Eligibility age (in years)	55 years
Minimum service period for eligibility (in years)	10 years
Expected contribution by employer in the next fiscal year	2.0
Change in projected benefit obligation
Projected benefit obligation at beginning of year	130		122
Service cost	3		3
Interest cost	6		6
Actuarial (gain) / loss	(8)		1
Benefits paid	(3)		(2)
Projected benefit obligation at end of year	128		130
Change in plan assets
Fair value of plan assets at beginning of period	0		0
Employer contributions	3		2
Benefits paid	(3)		(2)
Fair value of plan assets at end of period	0		0
Funded status at end of year	(128)		(130)
Amounts recognized in the consolidated balance sheets:
Long-term liabilities	(128)		(130)
Amounts recognized in accumulated other comprehensive income:
Prior service cost (credit)	8		8
Net loss	14		23
Weighted-average assumptions used to determine obligations at end of year:
Discount rate	4.25%		4.75%
Assumed health care cost trend rates:
Rate assumed for following year	8.50%		9.50%
Ultimate rate	5.00%		5.25%
Year ultimate rate reached	2020		2019
Postretirement Benefits Other Than Pensions | Midwest Generation LLC
Pension and Other Postretirement Benefits
Eligibility age (in years)	55 years
Minimum service period for eligibility (in years)	10 years
Expected contribution by employer in the next fiscal year	1.0
Change in projected benefit obligation
Projected benefit obligation at beginning of year	59		54
Service cost	1		2
Interest cost	3		2
Actuarial (gain) / loss	(3)		2
Benefits paid	(1)		(1)
Projected benefit obligation at end of year	59		59
Change in plan assets
Fair value of plan assets at beginning of period	0		0
Employer contributions	1		1
Benefits paid	(1)		(1)
Fair value of plan assets at end of period	0		0
Funded status at end of year	(59)		(59)
Amounts recognized in the consolidated balance sheets:
Long-term liabilities	(59)		(59)
Amounts recognized in accumulated other comprehensive income:
Prior service cost (credit)	10		11
Net loss	9		12
Weighted-average assumptions used to determine obligations at end of year:
Discount rate	4.25%		4.75%
Assumed health care cost trend rates:
Rate assumed for following year	8.50%		9.50%
Ultimate rate	5.00%		5.25%
Year ultimate rate reached	2020		2019
Postretirement Benefits Other Than Pensions | Homer City
Amounts recognized in the consolidated balance sheets:
Long-term liabilities	31
Postretirement Benefits Other Than Pensions | Other EME Subsidiaries
Change in projected benefit obligation
Projected benefit obligation at beginning of year	71	[2]	68	[2]
Service cost	2	[2]	1	[2]
Interest cost	3	[2]	4	[2]
Actuarial (gain) / loss	(5)	[2]	(1)	[2]
Benefits paid	(2)	[2]	(1)	[2]
Projected benefit obligation at end of year	69	[2]	71	[2]
Change in plan assets
Fair value of plan assets at beginning of period	0	[2]	0	[2]
Employer contributions	2	[2]	1	[2]
Benefits paid	(2)	[2]	(1)	[2]
Fair value of plan assets at end of period	0	[2]	0	[2]
Funded status at end of year	(69)	[2]	(71)	[2]
Amounts recognized in the consolidated balance sheets:
Long-term liabilities	(69)	[2]	(71)	[2]
Amounts recognized in accumulated other comprehensive income:
Prior service cost (credit)	(2)	[2]	(3)	[2]
Net loss	5	[2]	11	[2]
Weighted-average assumptions used to determine obligations at end of year:
Discount rate	4.25%	[2]	4.75%	[2]
Assumed health care cost trend rates:
Rate assumed for following year	8.50%	[2]	9.50%	[2]
Ultimate rate	5.00%	[2]	5.25%	[2]
Year ultimate rate reached	2020	[2]	2019	[2]
Employee Retirement Related Liabilities | Edison International
Pension and Other Postretirement Benefits
Employee retirement related liabilities assumed by Edison International	200
Union Employees | Edison International | Postretirement Benefits Other Than Pensions | Homer City
Amounts recognized in the consolidated balance sheets:
Long-term liabilities	20
Non-Union Employees | Edison International | Postretirement Benefits Other Than Pensions | Homer City
Amounts recognized in the consolidated balance sheets:
Long-term liabilities	$ 11

[1] Represents amount of EME's executive post retirement benefits liability assumed by EIX.

[2] Includes Homer City.