Derivative Instruments and Hedging Activities (Notional Values) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012 Edison Mission Group Inc. Interest Rate Contracts	Dec. 31, 2011 Edison Mission Group Inc. Interest Rate Contracts	Dec. 31, 2011 Edison Mission Group Inc. Foward Starting Interest Rate Contracts	Mar. 31, 2012 Edison Mission Group Inc. Foward Starting Interest Rate Contracts Convert Floating Rate Debt to Fixed 3.5429% Debt [Member]	Mar. 31, 2012 Edison Mission Group Inc. Foward Starting Interest Rate Contracts Convert Floating Rate Debt to Fixed 3.57% Debt [Member]	Mar. 31, 2012 Edison Mission Group Inc. Foward Starting Interest Rate Contracts Convert Floating Rate Debt to Fixed 4.0025% Debt [Member]	Mar. 31, 2012 Edison Mission Energy Foward Starting Interest Rate Contracts	Mar. 31, 2012 Electric Utility Electricity options, swaps and forwards in gigawatts per hour (GWh) Economic hedges GWh	Dec. 31, 2011 Electric Utility Electricity options, swaps and forwards in gigawatts per hour (GWh) Economic hedges GWh	Mar. 31, 2012 Electric Utility Natural gas options, swaps and forwards, Bcf Economic hedges Bcf	Dec. 31, 2011 Electric Utility Natural gas options, swaps and forwards, Bcf Economic hedges Bcf	Mar. 31, 2012 Electric Utility Congestion revenue rights Economic hedges GWh	Dec. 31, 2011 Electric Utility Congestion revenue rights Economic hedges GWh	Mar. 31, 2012 Electric Utility Tolling arrangements (GWh) Economic hedges GWh	Dec. 31, 2011 Electric Utility Tolling arrangements (GWh) Economic hedges GWh	Mar. 31, 2012 Competitive Power Generation Electricity Forwards/Futures, Sales, GWh Cash flow hedges GWh		Dec. 31, 2011 Competitive Power Generation Electricity Forwards/Futures, Sales, GWh Cash flow hedges GWh		Mar. 31, 2012 Competitive Power Generation Electricity Forwards/Futures, Sales, GWh Economic hedges GWh		Dec. 31, 2011 Competitive Power Generation Electricity Forwards/Futures, Sales, GWh Economic hedges GWh		Mar. 31, 2012 Competitive Power Generation Electricity Forwards/Futures, Sales, GWh Trading activities GWh	Dec. 31, 2011 Competitive Power Generation Electricity Forwards/Futures, Sales, GWh Trading activities GWh	Mar. 31, 2012 Competitive Power Generation Electricity Forwards/Futures, Purchases, GWh Cash flow hedges GWh	Dec. 31, 2011 Competitive Power Generation Electricity Forwards/Futures, Purchases, GWh Cash flow hedges GWh	Mar. 31, 2012 Competitive Power Generation Electricity Forwards/Futures, Purchases, GWh Economic hedges GWh	Dec. 31, 2011 Competitive Power Generation Electricity Forwards/Futures, Purchases, GWh Economic hedges GWh	Mar. 31, 2012 Competitive Power Generation Electricity Forwards/Futures, Purchases, GWh Trading activities GWh	Dec. 31, 2011 Competitive Power Generation Electricity Forwards/Futures, Purchases, GWh Trading activities GWh	Mar. 31, 2012 Competitive Power Generation Electricity Capacity, Sales, MW-Day (in thousands) Cash flow hedges MW		Dec. 31, 2011 Competitive Power Generation Electricity Capacity, Sales, MW-Day (in thousands) Cash flow hedges MW		Mar. 31, 2012 Competitive Power Generation Electricity Capacity, Sales, MW-Day (in thousands) Economic hedges MW	Dec. 31, 2011 Competitive Power Generation Electricity Capacity, Sales, MW-Day (in thousands) Economic hedges MW	Mar. 31, 2012 Competitive Power Generation Electricity Capacity, Sales, MW-Day (in thousands) Trading activities MW	Dec. 31, 2011 Competitive Power Generation Electricity Capacity, Sales, MW-Day (in thousands) Trading activities MW	Mar. 31, 2012 Competitive Power Generation Electricity Capacity, Purchases, MW-Day (in thousands) Cash flow hedges MW	Dec. 31, 2011 Competitive Power Generation Electricity Capacity, Purchases, MW-Day (in thousands) Cash flow hedges MW	Mar. 31, 2012 Competitive Power Generation Electricity Capacity, Purchases, MW-Day (in thousands) Economic hedges MW	Dec. 31, 2011 Competitive Power Generation Electricity Capacity, Purchases, MW-Day (in thousands) Economic hedges MW	Mar. 31, 2012 Competitive Power Generation Electricity Capacity, Purchases, MW-Day (in thousands) Trading activities MW		Dec. 31, 2011 Competitive Power Generation Electricity Capacity, Purchases, MW-Day (in thousands) Trading activities MW		Mar. 31, 2012 Competitive Power Generation Electricity Congestion, Purchases, GWh Cash flow hedges GWh	Dec. 31, 2011 Competitive Power Generation Electricity Congestion, Purchases, GWh Cash flow hedges GWh	Mar. 31, 2012 Competitive Power Generation Electricity Congestion, Purchases, GWh Economic hedges GWh		Dec. 31, 2011 Competitive Power Generation Electricity Congestion, Purchases, GWh Economic hedges GWh		Mar. 31, 2012 Competitive Power Generation Electricity Congestion, Purchases, GWh Trading activities GWh		Dec. 31, 2011 Competitive Power Generation Electricity Congestion, Purchases, GWh Trading activities GWh		Dec. 31, 2011 Competitive Power Generation Natural Gas Forwards/Futures, Sales, bcf Cash flow hedges Bcf	Dec. 31, 2011 Competitive Power Generation Natural Gas Forwards/Futures, Sales, bcf Economic hedges Bcf	Dec. 31, 2011 Competitive Power Generation Natural Gas Forwards/Futures, Sales, bcf Trading activities Bcf	Mar. 31, 2012 Competitive Power Generation Natural Gas Forwards/Futures, Purchases, bcf Cash flow hedges Bcf	Mar. 31, 2012 Competitive Power Generation Natural Gas Forwards/Futures, Purchases, bcf Economic hedges Bcf	Mar. 31, 2012 Competitive Power Generation Natural Gas Forwards/Futures, Purchases, bcf Trading activities Bcf	Mar. 31, 2012 Competitive Power Generation Fuel Oil Forwards/Futures, Purchases, Barrels Cash flow hedges bbl	Dec. 31, 2011 Competitive Power Generation Fuel Oil Forwards/Futures, Purchases, Barrels Cash flow hedges bbl	Mar. 31, 2012 Competitive Power Generation Fuel Oil Forwards/Futures, Purchases, Barrels Economic hedges bbl	Dec. 31, 2011 Competitive Power Generation Fuel Oil Forwards/Futures, Purchases, Barrels Economic hedges bbl	Mar. 31, 2012 Competitive Power Generation Fuel Oil Forwards/Futures, Purchases, Barrels Trading activities bbl	Dec. 31, 2011 Competitive Power Generation Fuel Oil Forwards/Futures, Purchases, Barrels Trading activities bbl	Apr. 30, 2012 Agreements for financing interests in projects Edison Mission Energy Foward Starting Interest Rate Contracts
Derivatives
Notional Volumes of Derivative Instruments								28,611.0	30,881.0	258.0	300.0	150,896.0	166,163.0	103,491.0	104,154.0	5,850.0	[1]	8,320.0	[1]	102.0	[2]	425.0	[2]	0	0	0	0	0	0	2,425.0	2,926.0	58,000.0	[3]	89,000.0	[3]	0	0	0	0	0	0	0	0	161,000.0	[3]	184,000.0	[3]	0	0	1,079.0	[4]	2,528.0	[4]	165,365.0	[4]	230,798.0	[4]	0.0	0.0	0.2	0.0	0.0	12.0	0	0	360,000.0	240,000.0	0	0
Notional Amount of Interest Rate Derivatives	$ 681	$ 644	$ 506				$ 502																																																															$ 139
Derivative, Variable Interest Rate				3.5429%	3.57%	4.0025%
Derivative, Lower Variable Interest Rate Range	0.79%	0.79%					3.5429%																																																															0.7825%
Derivative, Higher Variable Interest Rate Range	4.29%	4.29%					4.0025%																																																															2.96%

[1] EMG's hedge products include forward and futures contracts that qualify for hedge accounting.

[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 Interconnection, LLC Reliability Pricing Model (PJM 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.