Property, Plant and Equipment - Annual Depreciation Provisions as Percentage of Average Service Life (Details)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.79%	2.80%	2.73%
Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	6.11%	4.35%	5.37%
Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.14%	2.04%	2.07%
Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	7.01%	7.37%	6.98%
Exelon Generation Co L L C [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	6.11%	4.35%	5.37%
Commonwealth Edison Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.95%	2.99%	2.95%
PECO Energy Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.31%	2.36%	2.35%
PECO Energy Co [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.85%	1.89%	1.90%
PECO Energy Co [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	6.39%	6.06%	5.44%
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.69%	2.60%	2.61%
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.56%	2.30%	2.36%
Baltimore Gas and Electric Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	7.45%	8.30%	8.50%
Pepco Holdings LLC [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.81%	2.77%	2.61%
Pepco Holdings LLC [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.50%	1.55%	1.59%
Pepco Holdings LLC [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	7.36%	8.25%	6.30%
Potomac Electric Power Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.53%	2.47%	2.40%
Delmarva Power & Light Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.85%	2.86%	2.77%
Delmarva Power & Light Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.50%	1.55%	1.59%
Delmarva Power & Light Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	6.72%	6.24%	3.70%
Atlantic City Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	3.08%	2.94%	2.45%