Intangible Assets - Summary of Amortization Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense		$ 7	$ 7	$ 7
Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	[1]	22	135	430
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	[1]	$ 22	135	507
Unamortized Energy Contracts [Member] | Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	[1]		$ 0	$ 0

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