Derivative Instruments and Hedging Activities (Notional Values) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011 GWh		Dec. 31, 2010 GWh		Dec. 31, 2009 GWh
Edison Mission Energy | Interest Rate Contracts
Derivatives
Notional Amount of Interest Rate Derivatives	644		328
Derivative, Lower Variable Interest Rate Range	0.79%		3.175%
Derivative, Higher Variable Interest Rate Range	4.29%		4.29%
Edison Mission Energy | Foward Starting Interest Rate Contracts
Derivatives
Notional Amount of Interest Rate Derivatives	506
Derivative, Lower Variable Interest Rate Range	3.5429%
Derivative, Higher Variable Interest Rate Range	4.0025%
Electric Utility | Electricity options, swaps and forwards in gigawatts per hour (GWh) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	30,881		32,138
Electric Utility | Natural gas options, swaps and forwards, Bcf | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	300		250
Electric Utility | Congestion revenue rights | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	166,163		181,291
Electric Utility | Tolling arrangements (GWh) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	104,154		114,599
Competitive Power Generation | Energy trading activities, gross purchases and sales, GWh | Trading activities | Edison Mission Energy
Derivatives
Notional Volumes of Derivative Instruments	3,332		3,944		3,791
Competitive Power Generation | Electricity Forwards/Futures, Sales, GWh | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments	8,320	[1]	16,391	[1]
Competitive Power Generation | Electricity Forwards/Futures, Sales, GWh | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	425	[2]	0	[2]
Competitive Power Generation | Electricity Forwards/Futures, Sales, GWh | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	0		0
Competitive Power Generation | Electricity Forwards/Futures, Purchases, GWh | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments	0	[1]	0
Competitive Power Generation | Electricity Forwards/Futures, Purchases, GWh | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	0	[2]	475	[2]
Competitive Power Generation | Electricity Forwards/Futures, Purchases, GWh | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	2,926		3,039
Competitive Power Generation | Electricity Capacity, Sales, MW-Day (in thousands) | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments	0	[3]	182,000	[3]
Competitive Power Generation | Electricity Capacity, Sales, MW-Day (in thousands) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	0		0
Competitive Power Generation | Electricity Capacity, Sales, MW-Day (in thousands) | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	0	[3]	0	[3]
Competitive Power Generation | Electricity Capacity, Purchases, MW-Day (in thousands) | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments	0	[3]	0
Competitive Power Generation | Electricity Capacity, Purchases, MW-Day (in thousands) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	0		0
Competitive Power Generation | Electricity Capacity, Purchases, MW-Day (in thousands) | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	184,000	[3]	283,000
Competitive Power Generation | Electricity Congestion, Purchases, GWh | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments	0		0
Competitive Power Generation | Electricity Congestion, Purchases, GWh | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	2,528	[4]	1,007	[4]
Competitive Power Generation | Electricity Congestion, Purchases, GWh | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	230,798	[4]	175,669	[4]
Competitive Power Generation | Natural Gas Forwards/Futures, Sales, billion cubic feet | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments	0
Competitive Power Generation | Natural Gas Forwards/Futures, Sales, billion cubic feet | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	0
Competitive Power Generation | Natural Gas Forwards/Futures, Sales, billion cubic feet | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	0.2
Competitive Power Generation | Natural Gas Forwards/Futures, Purchases, billion cubic feet | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments			0
Competitive Power Generation | Natural Gas Forwards/Futures, Purchases, billion cubic feet | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments			0
Competitive Power Generation | Natural Gas Forwards/Futures, Purchases, billion cubic feet | Trading activities
Derivatives
Notional Volumes of Derivative Instruments			3.7
Competitive Power Generation | Fuel Oil Forwards/Futures, Purchases, Barrels | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments	0		0
Competitive Power Generation | Fuel Oil Forwards/Futures, Purchases, Barrels | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	240,000		240,000
Competitive Power Generation | Fuel Oil Forwards/Futures, Purchases, Barrels | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	0		0
Competitive Power Generation | Coal Forwards/Futures, Purchases, tons | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments			0
Competitive Power Generation | Coal Forwards/Futures, Purchases, tons | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments			0
Competitive Power Generation | Coal Forwards/Futures, Purchases, tons | Trading activities
Derivatives
Notional Volumes of Derivative Instruments			15,000

[1] EMG's hedge products include forward and futures contracts that qualify for hedge accounting. This category excludes power contracts for the coal plants which meet the normal purchases and sales exception and are accounted for on the accrual method.

[2] These positions adjust financial and physical positions, or day-ahead and real-time positions, to reduce costs or increase gross margin. The net sales positions of these categories are primarily related to hedge transactions that are not designated as cash flow hedges.

[3] EMG's hedge transactions for capacity result from bilateral trades. Capacity sold in the PJM Reliability Pricing Model (RPM) auction is not accounted for as a derivative.

[4] Congestion contracts include financial transmission rights, transmission congestion contracts or congestion revenue rights. These positions are similar to a swap, where the buyer is entitled to receive a stream of revenues (or charges) based on the hourly day-ahead price differences between two locations.