Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012 segment	Dec. 31, 2011
Summary of Significant Accounting Policies [Line Items]
Number of segments for financial reporting purposes	2
Cash Equivalents
Money market funds	$ 933	$ 1,300
Maximum maturity period of cash equivalent investments (in months)	3 months
Cash reclassified to accounts payable under cash management program	234	220
Restricted Cash and Deposits
Restricted deposits	89	25
Inventory
Coal, gas, fuel oil and other raw materials	138	143
Spare parts, materials and supplies	370	376
Total inventory	508	519
Edison Mission Energy | Letters of Credit
Restricted Cash and Deposits
Restricted deposits	48
Electric Utility
Summary of Significant Accounting Policies [Line Items]
Supply of electricity, area covered (square mile)	50,000
Wind Financing
Restricted Cash and Deposits
Restricted cash and cash equivalents	$ 97	$ 97