Debt and Credit Agreements - Commercial Paper Borrowings (Details) - Commercial Paper [Member] - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Short-term Debt [Line Items]
Commercial Paper	$ 365	$ 1,031
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.17%	0.25%
Corporate [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 0	$ 0
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 0	$ 340
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.00%	0.27%
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 33	$ 323
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.15%	0.23%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 0	$ 0
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Commercial Paper	0	0
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 332	$ 368
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.17%	0.24%
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 154	$ 35
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.17%	0.22%
Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 0	$ 146
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.00%	0.24%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 178	$ 187
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.18%	0.25%