Intangible Assets - Narrative (Details) - USD ($)		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 01, 2016	Mar. 24, 2016
Goodwill [Line Items]
Goodwill			$ 6,677,000,000	$ 6,677,000,000	$ 6,677,000,000	$ 2,672,000,000
Goodwill, Purchase Accounting Adjustments					(11,000,000)
Amortization of Intangible Assets				92,000,000	87,000,000	76,000,000
Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Goodwill			47,000,000	47,000,000	47,000,000	47,000,000
Amortization of Intangible Assets				83,000,000	79,000,000	69,000,000
Commonwealth Edison Co [Member]
Goodwill [Line Items]
Goodwill			2,625,000,000	2,625,000,000	2,625,000,000	2,625,000,000
Amortization of Intangible Assets				7,000,000	7,000,000	7,000,000
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount							30.00%
Pepco Holdings LLC [Member] | Predecessor [Member]
Goodwill [Line Items]
Goodwill		$ 1,406,000,000				1,406,000,000
Pepco Holdings LLC [Member] | Successor [Member]
Goodwill [Line Items]
Goodwill		0	4,005,000,000	4,005,000,000	4,005,000,000
Goodwill, Purchase Accounting Adjustments			(11,000,000)	0
Potomac Electric Power Company [Member]
Goodwill [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets								$ 1,700,000,000
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount							10.00%
Delmarva Power and Light Company [Member]
Goodwill [Line Items]
Goodwill			8,000,000	$ 8,000,000	8,000,000	8,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets								1,100,000,000
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount				50.00%			10.00%
Atlantic City Electric Company [Member]
Goodwill [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets								$ 1,200,000,000
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]			$ 35,000,000	35,000,000	22,000,000
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			35,000,000	35,000,000	22,000,000
Unamortized Energy Contracts [Member] | Commonwealth Edison Co [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			0	0	0
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] | Predecessor [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]	$ 0				0
Unamortized Energy Contracts [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]		$ 0	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] | 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	$ 0	$ 0
Constellation Energy Group LLC [Member] | Trade Names [Member]
Goodwill [Line Items]
Useful life				10 years

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