Supplemental Financial Information - Summary of Depreciation, Amortization, Accretion and Depletion (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
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				$ 3,293	$ 3,477	$ 2,227
Regulatory assets				478	407	170
Amortization of Intangible Assets				92	87	76
Nuclear fuel	[1]			1,096	1,159	1,116
ARO accretion	[2]			468	446	398
Total depreciation, amortization and accretion				5,427	5,576	3,987
Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				1,409	1,835	1,007
Regulatory assets				0	0	0
Amortization of Intangible Assets				83	79	69
Nuclear fuel	[1]			1,096	1,159	1,116
ARO accretion	[2]			468	446	397
Total depreciation, amortization and accretion				3,056	3,519	2,589
Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				777	708	635
Regulatory assets				73	67	72
Amortization of Intangible Assets				7	7	7
Nuclear fuel	[1]			0	0	0
ARO accretion	[2]			0	0	0
Total depreciation, amortization and accretion				850	775	707
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				261	244	240
Regulatory assets				25	26	20
Nuclear fuel	[1]			0	0	0
ARO accretion	[2]			0	0	0
Total depreciation, amortization and accretion				286	270	260
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				312	299	289
Regulatory assets				161	124	77
Nuclear fuel	[1]			0	0	0
ARO accretion	[2]			0	0	0
Total depreciation, amortization and accretion				473	423	366
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment			$ 325	457
Regulatory assets			190	218
Nuclear fuel	[1]		0	0
ARO accretion	[2]		0	0
Total depreciation, amortization and accretion			515	675
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment		$ 94				392
Regulatory assets		58				232
Nuclear fuel	[1]	0				0
ARO accretion	[2]	0				0
Total depreciation, amortization and accretion		152				624
Potomac Electric Power Company [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				203	175	164
Regulatory assets				118	120	92
Nuclear fuel	[1]			0	0	0
ARO accretion	[2]			0	0	0
Total depreciation, amortization and accretion				321	295	256
Delmarva Power and Light Company [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				124	110	103
Regulatory assets				43	47	45
Nuclear fuel	[1]			0	0	0
ARO accretion	[2]			0	0	0
Total depreciation, amortization and accretion				167	157	148
Atlantic City Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				89	82	76
Regulatory assets				57	83	99
Nuclear fuel	[1]			0	0	0
ARO accretion	[2]			0	0	0
Total depreciation, amortization and accretion				146	165	175
Unamortized Energy Contracts [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			35	35	22
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			35	35	22
Unamortized Energy Contracts [Member] | Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			0	0	0
Unamortized Energy Contracts [Member] | PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			0	0	0
Unamortized Energy Contracts [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			0	0	0
Unamortized Energy Contracts [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]		0	0
Unamortized Energy Contracts [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]	0				0
Unamortized Energy Contracts [Member] | Potomac Electric Power Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			0	0	0
Unamortized Energy Contracts [Member] | Delmarva Power and Light Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			0	0	0
Unamortized Energy Contracts [Member] | Atlantic City Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			0	0	0
Other Intangible Assets [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				57	52	54
Other Intangible Assets [Member] | Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				48	44	47
Other Intangible Assets [Member] | Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				0	0	0
Other Intangible Assets [Member] | PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				0	0	0
Other Intangible Assets [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				0	0	0
Other Intangible Assets [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets			$ 0	0
Other Intangible Assets [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets		$ 0				0
Other Intangible Assets [Member] | Potomac Electric Power Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				0	0	0
Other Intangible Assets [Member] | Delmarva Power and Light Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				0	0	0
Other Intangible Assets [Member] | Atlantic City Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				$ 0	$ 0	$ 0

[1] Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[2] Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[3] Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income