Income Taxes (Deferred Tax Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Deferred tax assets
Accrued charges and liabilities	$ 234		$ 303
Net operating loss carryforwards	841		326
Production tax and other credit carryforwards	254		194
Derivative instruments	49		49
Other	6		0
Total deferred tax assets, gross	1,384		872
Valuation allowance	(444)		0
Net deferred tax assets	940		872
Deferred tax liabilities
Property, plant and equipment - basis differences	989		638
Deferred investment tax credit	4		5
State taxes	28		20
Other	0		6
Total	1,021		669
Deferred tax assets and (liabilities), net	(81)		203
Classification of net accumulated deferred income taxes
Included in other assets	0		205
Included in current liabilities	0		2
Deferred taxes and tax credits	81		0
Change in valuation allowance on deferred tax asset	(6)		0	0
Non-cash distribution to parent	222	[1]
Tax payments made without corresponding statutory tax	120
Federal
Classification of net accumulated deferred income taxes
Tax credit carryforwards	254
Federal | Expiring in 2031 and 2032
Classification of net accumulated deferred income taxes
Net operating loss carryforwards	2,334
Federal | Expiring Between 2029 and 2032
Classification of net accumulated deferred income taxes
Tax credit carryforwards	239
State | Expiring Between 2022 and 2032
Classification of net accumulated deferred income taxes
Net operating loss carryforwards	2,158
Midwest Generation LLC
Deferred tax assets
State taxes	0		3
Deferred income	2		1
Accrued charges and liabilities	16		9
Net operating loss carryforwards	0		19
Derivative instruments	24		9
Impairment of loan to affiliate - tax	539		0
Property, plant and equipment - basis differences	0		15
Total deferred tax assets, gross	581		56
Valuation allowance	(533)		0
Net deferred tax assets	48		56
Deferred tax liabilities
Property, plant and equipment - basis differences	45		0
State taxes	3		0
Total	48		0
Deferred tax assets and (liabilities), net	0		56
Classification of net accumulated deferred income taxes
Included in current assets	0		14
Included in other assets	0		42
Change in valuation allowance on deferred tax asset	(12)		0	0
Non-cash distribution to parent	106	[2]
Midwest Generation LLC | Federal | Expiring in 2031 and 2032
Classification of net accumulated deferred income taxes
Net operating loss carryforwards	291
Midwest Generation LLC | State | Expiring Between 2025 and 2032
Classification of net accumulated deferred income taxes
Net operating loss carryforwards	199
Other Long-Term Assets
Classification of net accumulated deferred income taxes
Income tax allocation agreements	18		86
Payables to Affiliates
Classification of net accumulated deferred income taxes
Income tax allocation agreements	(33)		(174)
Other Long-Term Liabilities
Classification of net accumulated deferred income taxes
Income tax allocation agreements	(21)
Accumulated other comprehensive loss
Deferred tax assets
Valuation allowance	(6)
Accumulated other comprehensive loss | Midwest Generation LLC
Deferred tax assets
Valuation allowance	(12)	[3]
Hypothetical Tax Return | Midwest Generation LLC
Classification of net accumulated deferred income taxes
Non-cash distribution to parent	106
Provision (Benefit) for Income Taxes
Classification of net accumulated deferred income taxes
Change in valuation allowance on deferred tax asset	438
Provision (Benefit) for Income Taxes | Midwest Generation LLC
Classification of net accumulated deferred income taxes
Change in valuation allowance on deferred tax asset	521	[3]
Edison International
Classification of net accumulated deferred income taxes
Tax benefits generated and utilized by EIX under tax allocation agreement	102
Tax benefits generated but not yet utilized by EIX under tax allocation agreement	1,071
Edison International | Capistrano Wind Holdings
Classification of net accumulated deferred income taxes
Tax benefits generated under tax allocation agreement	40
Edison International | Capistrano Wind, LLC
Classification of net accumulated deferred income taxes
Tax benefits generated and utilized by EIX under tax allocation agreement	$ 16

[1] During the fourth quarter of 2012, EME recorded a non-cash distribution to EIX related to the tax-allocation agreement. See Note 7—Income Taxes—EME—Current and Deferred Taxes.

[2] During 2012, Midwest Generation recorded a non-cash distribution to its parent related to the tax-allocation agreement. See Note 7—Income Taxes—Midwest Generation—Current and Deferred Taxes.

[3] Midwest Generation recorded a deferred tax valuation allowance during the fourth quarter of 2012 related to the impairment of its intercompany loan with EME. For further discussion, see "Item 8. Combined Notes to Consolidated Financial Statements—Note 7. Income Taxes."