Mergers, Acquisitions and Dispositions - Summary of Asset Divestitures (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Long Lived Assets Held-for-sale [Line Items]
Gain (Loss) on Sale of Assets and Asset Impairment Charges	$ 437	$ 13	$ (7)
Fore River [Member]
Long Lived Assets Held-for-sale [Line Items]
Percent Owned	100.00%
Net Generation Capacity	726,000,000
West Valley [Member]
Long Lived Assets Held-for-sale [Line Items]
Percent Owned	100.00%
Net Generation Capacity	185,000,000
Keystone [Member]
Long Lived Assets Held-for-sale [Line Items]
Percent Owned	41.98%
Net Generation Capacity	714,000,000
Conemaugh [Member]
Long Lived Assets Held-for-sale [Line Items]
Percent Owned	31.28%
Net Generation Capacity	532,000,000
Safe Harbor [Member]
Long Lived Assets Held-for-sale [Line Items]
Percent Owned	66.70%
Net Generation Capacity	278,000,000
Quail Run [Member]
Long Lived Assets Held-for-sale [Line Items]
Gain (Loss) on Sale of Assets and Asset Impairment Charges	412
Percent Owned	100.00%
Net Generation Capacity	488,000,000
Exelon Generation Co L L C [Member]
Long Lived Assets Held-for-sale [Line Items]
Gain (Loss) on Sale of Assets and Asset Impairment Charges	$ 437	$ 13	$ (7)