Early Nuclear Plant Retirements Early Nuclear Plant Retirements table (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Regulatory Assets		$ 11,388	$ 6,824
Asset Retirement Obligation, Accretion Expense	[1]	446	398	$ 345
Property, plant and equipment		3,477	2,227	2,080
Nuclear Fuel Amortization	[2]	1,159	1,116	1,073
Quad Cities [Member]
Property, Plant and Equipment [Line Items]
Asset Retirement Obligation		565
Facility Closing [Member]
Property, Plant and Equipment [Line Items]
Other Expenses		688
Delmarva Power and Light Company [Member]
Property, Plant and Equipment [Line Items]
Regulatory Assets		348	371
Asset Retirement Obligation, Accretion Expense	[1]	0	0	0
Property, plant and equipment		110	103	94
Nuclear Fuel Amortization	[2]	0	0	0
Commonwealth Edison Co [Member]
Property, Plant and Equipment [Line Items]
Regulatory Assets		1,167	1,113
Asset Retirement Obligation, Accretion Expense	[1]	0	0	0
Property, plant and equipment		708	635	588
Nuclear Fuel Amortization	[2]	0	0	$ 0
Accelerated Depreciation Costs of Non AMI Meters [Member] | Commonwealth Edison Co [Member]
Property, Plant and Equipment [Line Items]
Regulatory Assets		162	137
Deferred Income Tax Transmission Related [Member] | Delmarva Power and Light Company [Member]
Property, Plant and Equipment [Line Items]
Regulatory Assets		20	18
Deferred Income Tax Transmission Related [Member] | Commonwealth Edison Co [Member]
Property, Plant and Equipment [Line Items]
Regulatory Assets		22	$ 15
Recoverable Smart Meter Related Costs [Member] | Delmarva Power and Light Company [Member]
Property, Plant and Equipment [Line Items]
Regulatory Assets		$ 41

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

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