Property, Plant and Equipment - Annual Depreciation Provisions as Percentage of Average Service Life (Details)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.80%	2.73%	2.75%
Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	4.35%	5.37%	4.36%
Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.04%	2.07%	2.10%
Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	7.37%	6.98%	7.05%
Exelon Generation Co L L C [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	4.35%	5.37%	4.36%
Commonwealth Edison Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.99%	2.95%	2.99%
PECO Energy Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.36%	2.35%	2.37%
PECO Energy Co [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.89%	1.90%	1.89%
PECO Energy Co [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	6.06%	5.44%	5.47%
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.60%	2.61%	2.58%
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.30%	2.36%	2.33%
Baltimore Gas and Electric Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	8.30%	8.50%	8.64%
Pepco Holdings LLC [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.77%	2.61%	2.63%
Pepco Holdings LLC [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.55%	1.59%	2.07%
Pepco Holdings LLC [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	8.25%	6.30%	6.50%
Potomac Electric Power Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.47%	2.40%	2.35%
Delmarva Power & Light Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.86%	2.77%	2.75%
Delmarva Power & Light Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.55%	1.59%	2.07%
Delmarva Power & Light Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	6.24%	3.70%	4.14%
Atlantic City Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.94%	2.45%	2.46%