Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended					3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 IRS Examination	Jun. 30, 2013 Midwest Generation LLC	Dec. 31, 2012 Midwest Generation LLC	Jun. 30, 2013 Edison International	Jun. 30, 2012 Edison International	Jun. 30, 2013 Edison International	Jun. 30, 2012 Edison International	Dec. 31, 2012 Hypothetical Tax Return Midwest Generation LLC
Income Tax Disclosures:
State tax expense (benefit)						$ 0	$ 2	$ 1	$ 5
Net tax allocation payments received under tax allocation agreement	6
Noncash distribution of tax benefits to parent		222								106
Valuation allowance	549	444		593	533
Estimated potential future federal tax payment as of the balance sheet date, including interest and penalties, based on a proposed adjustment			$ 203
Penalty for understatement of tax liability (as a percent)			40.00%