Commitments and Contingencies (Contingencies) (Details) (USD $)	1 Months Ended			9 Months Ended	1 Months Ended		9 Months Ended	1 Months Ended	9 Months Ended			9 Months Ended		9 Months Ended			1 Months Ended			9 Months Ended	1 Months Ended	9 Months Ended	1 Months Ended		9 Months Ended
	Jun. 30, 2010	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Nuclear Insurance	Oct. 31, 2011 Malibu Fire Order Instituting Investigation	Oct. 31, 2011 Alleged violations of PSD requirements and New Source Performance Standards of the CAA private_environmental_organization	Sep. 30, 2012 Edison International sites	Dec. 31, 2011 Southern California Edison	Sep. 30, 2012 Southern California Edison sites	Sep. 30, 2011 Southern California Edison	Sep. 15, 2012 Southern California Edison	Sep. 30, 2012 Southern California Edison San Onofre (nuclear) generator	Mar. 31, 2012 Southern California Edison San Onofre (nuclear) heat_transfer_tube	Sep. 30, 2012 Southern California Edison Nuclear Insurance	Sep. 30, 2012 Southern California Edison Nuclear Insurance San Onofre and Palo Verde	Sep. 30, 2012 Southern California Edison Outage, Inspection and Repair Issues San Onofre (nuclear) H	Oct. 30, 2011 Southern California Edison Malibu Fire Order Instituting Investigation	Jan. 31, 2012 Midwest Generation LLC. claims	Oct. 31, 2011 Midwest Generation LLC. claims	Sep. 30, 2012 Midwest Generation LLC. sites	Aug. 31, 2009 Midwest Generation LLC. Violation of certain operating permit requirements facilities	Sep. 30, 2012 Midwest Generation LLC. Violation of certain operating permit requirements claims	Jan. 31, 2011 Homer City Violations of the PSD and Title V provisions of the CAA owners residents	Feb. 29, 2012 Homer City Alleged violations of emissions standards and limitations under the CAA and the Pennsylvania Air Pollution Control Act	Sep. 30, 2012 SCE and other owners of San Onofre and Palo Verde Nuclear Insurance
Contingencies
Number of coal-fired electric generating stations																					6
Penalties sought, per violation, per day, minimum end of range																					$ 25,000		$ 32,500
Penalties sought, per violation, per day, maximum end of range																					37,500		37,500
Number of fully dismissed claims in the complaint filed by the US EPA and the State of Illinois																						9
Number of claims in the complaint filed by the US EPA and the State of Illinois																						10
Number of complaints filed asserting claims of nuisance, negligence, trespass, and strict liability																		2
Similar number of complaints previously filed asserting claims of nuisance, negligence, trespass, and strict liability that were dismissed																			2
Number of plaintiffs						4																	2
Number of prior owners of facilities																							2
Notice of intent to sue, notice time period																								60 days
Number of steam generators replaced (in generators)												4
Heat transfer tubes with water leak (in heat transfer tubes)													1
Reduced power level of operation (as a percentage)																70.00%
Term of reduced power level of operation (in months)																5 months
Authorized expenditures																525,000,000
Authorized expenditures, after adjustments for inflation																665,000,000
Ownership percentage (as a percent)												78.21%
Costs incurred to date																594,000,000
Construction work in progress																95,000,000
Authorized expenditures by authoritative body, market costs incurred																221,000,000
Annual revenue requirement request, nuclear fuel-related and decommissioning costs																170,000,000
Incremental inspection and repair costs																96,000,000
Collected revenue, based on current authorized revenue requirements																625,000,000
Annual revenue requirement request																820,000,000
Direct operating and maintenance costs, depreciation and return on investment																650,000,000
Rate base																1,200,000,000
Net investment and inventory associated with plant																2,100,000,000
Term of outage for which notification is required (in months)																9 months
Required term, from notice of investigation to remove revenue requirements from customer rates																45 days
Continuous hours of operation, after which rates may be readjusted																100
Steam generators, warranted period																20 years
MHI's limited liability under purchase agreement, excluding consequential damages																138,000,000
Invoiced amount to MHI																45,000,000
Damages sought					99,000,000			98,000,000									50,000,000
Identified material sites for environmental remediation (in number of sites)							27		25											2
Identified material sites, minimum amount of upper end of range of costs							1,000,000
Minimum liability for environmental remediation							121,000,000		113,000,000			78,000,000
Immaterial sites for environmental remediation (in number of sites)									33
Immaterial sites, range of liability, minimum									3,000,000
Environmental remediation liability									116,000,000
Regulatory assets		5,677,000,000	5,466,000,000						113,000,000
Portion of recorded liability recoverable from incentive mechanism									31,000,000
Percentage of environmental remediation costs recoverable through an incentive mechanism (as a percent)									90.00%
Liability incurred at majority of the remaining sites through customer rates									82,000,000
Environmental remediation costs to be recovered (as a percent)									100.00%
Amount that cleanup costs could exceed recorded liability for identified material sites									185,000,000
Amount that cleanup costs could exceed recorded liability for immaterial sites									6,000,000
Maximum expected period for cleanup of identified sites (in years)									30 years
Expected annual environmental remediation costs, low end of range									7,000,000
Expected annual environmental remediation costs, high end of range									14,000,000
Environmental remediation costs									5,000,000	9,000,000
Federal limit on public liability claims from nuclear incident, approximate				12,600,000,000
Private primary insurance purchased																									375,000,000
Maximum deferred insurance premium per each nuclear incident														235,000,000
Maximum yearly assessment per nuclear incident														35,000,000
Loss limit, property damage insurance															500,000,000
Loss limit, property damage insurance, federal minimum requirement															1,100,000,000
Limit on assessment of retrospective premium adjustments, per year, approximate														49,000,000
Insurance coverage for wildfire liabilities Limit											550,000,000
Self insurance retention per wildfire occurence											10,000,000
Amount of damages, decision by US Court of Federal Claims, spent nuclear fuel litigation	$ 142,000,000