Impairment of Long-lived Assets - Narrative (Details) - USD ($) $ in Millions				1 Months Ended	12 Months Ended
		May 31, 2014	Feb. 26, 2014	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Impairment charges					$ 24
Interest costs incurred	[1],[2]				1,678	$ 1,170	$ 1,144
Estimated residual value of leased assets					356	639
Proceeds From Lease Termination			$ 335		360
Capital leases net investment in direct financing leases writeoff			$ 336			352
Pre Tax Loss						1
Exelon Generation Co L L C [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Carrying amount of long lived assets to be written down		$ 151			60	1,000
Assets held for sale		65			24		556
Impairment charges		$ 86		$ 119	36	450	15
Interest costs incurred	[1],[2]				472	445	419
Baltimore Gas and Electric Company [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Interest costs incurred	[1]				$ 114	113	118
Constellation Energy Group LLC [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Impairment charges						$ 5	$ 124

[1] Successor PredecessorPHIMarch 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 For the Year Ended December 31, 2014Total incurred interest(b)$207 $68 $289 $277Credits to AFUDC debt and equity35 10 23 21

[2] Successor PredecessorPHIMarch 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 For the Year Ended December 31, 2014Total incurred interest(b)$207 $68 $289 $277Credits to AFUDC debt and equity35 10 23 21