Debt and Credit Agreements - Commercial Paper Borrowings (Details) - Commercial Paper [Member] - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Commercial Paper	$ 19	$ 870
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.15%	2.25%
Parent Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 0	$ 136
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.00%	1.92%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 0	$ 320
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.00%	1.84%
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 0	$ 130
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.00%	2.38%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 0	$ 76
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.00%	2.46%
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 19	$ 208
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.15%
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 14	$ 82
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.15%	2.56%
Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 0	$ 56
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.00%	2.02%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 5	$ 70
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.15%	2.43%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Commercial Paper	$ 0	$ 0
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.00%	0.00%