Derivative Instruments and Hedging Activities (Notional Values) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Edison Mission Energy | Interest Rate Contracts
Derivatives
Notional Amount of Interest Rate Derivatives	$ 703		$ 644
Derivative, Lower Variable Interest Rate Range	0.79%		0.79%
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	$ 641		$ 506
Derivative, Lower Variable Interest Rate Range	0.7825%
Derivative, Higher Variable Interest Rate Range	4.0025%
Edison Mission Energy | Foward Starting Interest Rate Contracts | Convert Floating Rate Debt to Fixed 3.5429% Debt [Member]
Derivatives
Derivative, Lower Variable Interest Rate Range			3.5429%
Edison Mission Energy | Foward Starting Interest Rate Contracts | Convert Floating Rate Debt to Fixed 3.57% Debt [Member]
Derivatives
Derivative, Higher Variable Interest Rate Range			3.57%
Edison Mission Energy | Foward Starting Interest Rate Contracts | Convert Floating Rate Debt to Fixed 4.0025% Debt [Member]
Derivatives
Derivative, Higher Variable Interest Rate Range			4.0025%
Electric Utility | Electricity options, swaps and forwards (GWh) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	26,597.0		30,881.0
Electric Utility | Natural gas options, swaps and forwards (bcf) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	213.0		300.0
Electric Utility | Congestion revenue rights (GWh) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	136,863.0		166,163.0
Electric Utility | Tolling arrangements (GWh) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	102,819.0		104,154.0
Competitive Power Generation | Electricity Forwards/Futures, Sales (GWh) | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments	4,630.0	[1]	8,320.0	[1]
Competitive Power Generation | Electricity Forwards/Futures, Sales (GWh) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	116.0	[2]	425.0	[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		0
Competitive Power Generation | Electricity Forwards/Futures, Purchases (GWh) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	0		0
Competitive Power Generation | Electricity Forwards/Futures, Purchases (GWh) | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	2,201.0		2,926.0
Competitive Power Generation | Electricity Capacity, Sales (GW-Day) | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments	37	[3]	89	[3]
Competitive Power Generation | Electricity Capacity, Sales (GW-Day) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	0		0
Competitive Power Generation | Electricity Capacity, Sales (GW-Day) | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	0		0
Competitive Power Generation | Electricity Capacity, Purchases (GW-Day) | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments	0		0
Competitive Power Generation | Electricity Capacity, Purchases (GW-Day) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	0		0
Competitive Power Generation | Electricity Capacity, Purchases (GW-Day) | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	134.0	[3]	184.0	[3]
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	287.0	[4]	2,528.0	[4]
Competitive Power Generation | Electricity Congestion, Purchases (GWh) | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	331,418.0	[4]	230,798.0	[4]
Competitive Power Generation | Natural Gas Forwards/Futures, Purchases (bcf) | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments	0
Competitive Power Generation | Natural Gas Forwards/Futures, Purchases (bcf) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments	0
Competitive Power Generation | Natural Gas Forwards/Futures, Purchases (bcf) | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	1.7
Competitive Power Generation | Natural Gas Forwards/Futures, Sales (bcf) | Cash flow hedges
Derivatives
Notional Volumes of Derivative Instruments			0
Competitive Power Generation | Natural Gas Forwards/Futures, Sales (bcf) | Economic hedges
Derivatives
Notional Volumes of Derivative Instruments			0
Competitive Power Generation | Natural Gas Forwards/Futures, Sales (bcf) | Trading activities
Derivatives
Notional Volumes of Derivative Instruments			0.2
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	240,000.0		240,000.0
Competitive Power Generation | Fuel Oil Forwards/Futures, Purchases (barrels) | Trading activities
Derivatives
Notional Volumes of Derivative Instruments	20,000.0		0

[1] EME'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] EME'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.