Significant Accounting Policies - Summary of Total Interest Incurred, Capitalized and Credits to AFUDC (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1],[2]			$ 1,678	$ 1,170	$ 1,144
Capitalized interest	[2]			108	79	63
Credits to AFUDC debt and equity	[2]			98	44	37
Exelon Generation Co L L C [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1],[2]			472	445	419
Capitalized interest	[2]			107	79	63
Credits to AFUDC debt and equity	[2]			0	0	0
Commonwealth Edison Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			469	336	323
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				22	9	5
PECO Energy Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			127	116	115
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				11	7	8
Baltimore Gas and Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			114	113	118
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				30	28	24
Potomac Electric Power Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred				137	131	121
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				29	19	16
Delmarva Power and Light Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred				52	51	49
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				7	2	3
Atlantic City Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred				65	65	65
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				$ 9	2	2
Predecessor [Member] | Pepco Holdings LLC [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred		$ 68			289	277
Credits to AFUDC debt and equity		$ 10			$ 23	$ 21
Successor [Member] | Pepco Holdings LLC [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred			$ 207
Credits to AFUDC debt and equity			$ 35

[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