Mergers, Acquisitions and Dispositions - Summary of Major Classes of Assets and Liabilities Held for Sale (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Significant Acquisitions and Disposals [Line Items]
Total assets held for sale	$ 147		$ 14
Accrued expenses	1,539		1,633
Other current liabilities	1,123		858
Electricity Generation Plant, Non-Nuclear [Member]
Significant Acquisitions and Disposals [Line Items]
Property, plant and equipment, net	143	[1]
Inventory	4
Total assets held for sale	147
Accrued expenses	1
Other current liabilities	4
Total liabilities held for sale	5	[2]
Asset impairment charges	$ 50

[1] The total aggregate book value of property, plant and equipment is net of a $50 million pre-tax impairment loss recorded within Operating and maintenance expense on Exelon’s and Generation’s Statements of Operations and Comprehensive Income. See Note 8 — Impairment of Long-Lived Assets for further information.

[2] Included within Other current liabilities on Exelon's and Generation's Consolidated Balance Sheets.