Property, Plant and Equipment Property, Plant and Equipment- Narrative (Details)	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	4.36%	[1]	5.94%	[1]	3.47%
Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.75%		2.73%		2.83%
Exelon Generation Co L L C [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	4.36%		5.94%		3.47%
Commonwealth Edison Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.99%		3.03%		3.03%
Potomac Electric Power Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.35%		2.17%		2.13%
Atlantic City Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.46%		2.45%		2.46%

[1] See Note 8 — Early Nuclear Plant Retirements for additional information on the accelerated net depreciation and amortization of Clinton, Quad Cities and TMI.