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, 2017	Dec. 31, 2016	Dec. 31, 2015
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			$ 1,658	$ 1,678	$ 1,170
Capitalized interest				63	108	79
Credits to AFUDC debt and equity				108	98	44
Exelon Generation Co L L C [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			502	472	445
Capitalized interest				63	107	79
Credits to AFUDC debt and equity				0	0	0
Commonwealth Edison Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			369	469	336
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				20	22	9
PECO Energy Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			130	127	116
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				12	11	7
Baltimore Gas and Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			111	114	113
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				22	30	28
Potomac Electric Power Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			133	137	131
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				34	29	19
Delmarva Power and Light Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			54	52	51
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				10	7	2
Atlantic City Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			64	65	65
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				9	9	$ 2
Predecessor [Member] | Pepco Holdings LLC [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]	$ 68			289
Credits to AFUDC debt and equity		$ 10			$ 23
Successor [Member] | Pepco Holdings LLC [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]		$ 207	263
Credits to AFUDC debt and equity			$ 35	$ 54

[1] (a)Includes interest expense to affiliates.