Mergers, Acquisitions, and Dispositions - Assets Disposition Table (Details) (USD $)	0 Months Ended
	Jan. 21, 2015	Mar. 31, 2015	Dec. 31, 2014
Assets Disposition Table [Line Items]
Total assets held for sale		$ 1,000,000	$ 147,000,000
Accrued expenses		1,230,000,000	1,539,000,000
Other current liabilities		1,018,000,000	1,123,000,000
Exelon Generation Co L L C [Member]
Assets Disposition Table [Line Items]
Proceeds from Sale of Productive Assets	1,800,000,000
Total assets held for sale		1,000,000	147,000,000
Accrued expenses		694,000,000	886,000,000
Other current liabilities		532,000,000	605,000,000
Proceed from sale of asset net of tax	$ 1,400,000,000