Property, Plant and Equipment Property, Plant and Equipment- Annual Depreciation Provisions as Percentage of Average Service Life (Details)	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.75%		2.73%		2.83%
Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	4.36%	[1]	5.94%	[1]	3.47%
Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.10%		2.17%		2.17%
Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	7.05%		7.41%		7.79%
PECO Energy Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.37%		2.32%		2.39%
PECO Energy Co [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.89%		1.82%		1.87%
PECO Energy Co [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	5.47%		5.11%		5.16%
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.58%		2.56%		2.62%
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.33%		2.45%		2.50%
Baltimore Gas and Electric Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	8.64%		9.45%		10.35%
Pepco Holdings LLC [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.63%		2.52%		2.48%
Pepco Holdings LLC [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.07%		2.57%		2.55%
Pepco Holdings LLC [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	6.50%		8.12%		5.19%
Delmarva Power and Light Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.75%		2.49%		2.44%
Delmarva Power and Light Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.07%		2.57%		2.55%
Delmarva Power and Light Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	4.14%		4.99%		4.24%

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