Intangible Assets - Summary of Amortization Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 24, 2016
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense		$ (109)	$ (237)	$ (336)
Potomac Electric Power Company [Member]
Finite-Lived Intangible Assets [Line Items]
Fresh-Start Adjustment, Increase (Decrease), Goodwill					$ 400
Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense		63	83	79
Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense		7	7	7
PHI Service Co Affiliate [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense		(188)	(336)	(430)
Delmarva Power & Light Company [Member]
Finite-Lived Intangible Assets [Line Items]
Fresh-Start Adjustment, Increase (Decrease), Goodwill					$ 300
Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Power Contracts Emission Credits	[1]	14	35	35
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Power Contracts Emission Credits	[1]	$ 14	$ 35	$ 35

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