Impairment of Long-lived Assets - Components of Net Investment in Long-term Leases (Details) - USD ($) $ in Millions				1 Months Ended	3 Months Ended		6 Months Ended	12 Months Ended
		May 31, 2014	Feb. 26, 2014	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Impairment or Disposal of Tangible Assets Disclosure [Abstract]
Capital Leases, Net Investment in Direct Financing Leases, Unguaranteed Residual Values of Leased Property					$ 356			$ 356	$ 639
Less: unearned income									287
Net investment in long-term leases	[1]								358
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Tangible Asset Impairment Charges								24
Capital Leases, Net Investment in Direct Financing Leases, Unguaranteed Residual Values of Leased Property					356			356	639
Proceeds From Lease Termination			$ 335					360
Gain (Loss) on Contract Termination								4
Exelon Generation Co L L C [Member]
Impairment or Disposal of Tangible Assets Disclosure [Abstract]
Net investment in long-term leases	[1]								6
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Tangible Asset Impairment Charges		$ 86		$ 119				36	450	$ 15
Assets held for sale		$ 65			24			$ 24		556
Gain (Loss) on Disposition of Property Plant Equipment					$ 69	$ 10	$ 32
Constellation Energy Group LLC [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Tangible Asset Impairment Charges									$ 5	$ 124

[1] Represents direct financing lease investments.