Intangible Assets - Narrative (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	Nov. 30, 2016	Mar. 24, 2016	Dec. 31, 2008
Goodwill [Line Items]
Goodwill			$ 6,677	$ 6,677	$ 2,672	$ 2,672
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets								$ 4,005
Goodwill, Purchase Accounting Adjustments				(11)
Amortization of Intangible Assets				87	76	179
Finite lived intangible assets gross			1,225	1,225
Commonwealth Edison Co [Member]
Goodwill [Line Items]
Goodwill			2,625	2,625	2,625	2,625
Amortization of Intangible Assets				7	7	7
Current alternative or renewable energy credits			0	0	5
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount							30.00%
Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Goodwill			47	47	47	47
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets						50
Amortization of Intangible Assets				79	69	179
Current alternative or renewable energy credits			317	317	251
Alternative Or Renewable Energy Credits Noncurrent			29	29	56
PECO Energy Co [Member]
Goodwill [Line Items]
Current alternative or renewable energy credits			1	1	2
Pepco Holdings LLC [Member] | Predecessor [Member]
Goodwill [Line Items]
Goodwill		$ 1,406			1,406	1,407
Pepco Holdings LLC [Member] | Successor [Member]
Goodwill [Line Items]
Goodwill		0	4,005	4,005
Goodwill, Purchase Accounting Adjustments			(11)
Potomac Electric Power Company [Member]
Goodwill [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets								1,700
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount							10.00%
Delmarva Power and Light Company [Member]
Goodwill [Line Items]
Goodwill			8	8	8	8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets								1,100
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount							10.00%		50.00%
Atlantic City Electric Company [Member]
Goodwill [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets								$ 1,200
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount							10.00%
Unamortized Energy Contracts [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			35	22	135
Unamortized Energy Contracts [Member] | Commonwealth Edison Co [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			0	0	0
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			35	22	135
Unamortized Energy Contracts [Member] | PECO Energy Co [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			0	0	0
Unamortized Energy Contracts [Member] | Pepco Holdings LLC [Member]
Goodwill [Line Items]
Finite lived intangible assets gross			(1,515)	(1,515)
Unamortized Energy Contracts [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]	$ 0
Unamortized Energy Contracts [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]		0
Unamortized Energy Contracts [Member] | Potomac Electric Power Company [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			0	0	0
Unamortized Energy Contracts [Member] | Potomac Electric Power Company [Member] | Predecessor [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]				0	0
Unamortized Energy Contracts [Member] | Delmarva Power and Light Company [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			0	0	0
Unamortized Energy Contracts [Member] | Atlantic City Electric Company [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			0
Unamortized Energy Contracts [Member] | Atlantic City Electric Company [Member] | Predecessor [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]				$ 0	$ 0
Constellation Energy Group LLC [Member] | Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Finite lived intangible assets gross	[2],[3]		1,499	$ 1,499
Constellation Energy Group LLC [Member] | Trade Names [Member]
Goodwill [Line Items]
Useful life				10 years
Constellation Energy Group LLC [Member] | Trade Names [Member] | Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Finite lived intangible assets gross	[3]		$ 243	$ 243

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

[2] Includes unamortized energy contract assets and liabilities on Exelon's and Generation's Consolidated Balance Sheets. Excludes $10 million of other miscellaneous unamortized energy contracts that have been acquired at various points in time. The estimated amortization for these miscellaneous unamortized energy contracts is $(9) million, $(7) million, $(6) million, $(2) million and $4 million for 2017, 2018, 2019, 2020 and 2021, respectively.

[3] On March 12, 2012, Constellation merged into Exelon with Exelon continuing as the surviving corporation pursuant to the transactions contemplated by the Agreement and Plan of Merger. Since the merger transaction, Generation includes the former Constellation generation and customer supply operations.