Debt and Credit Agreements - Commercial Paper Borrowings (Details) - Commercial Paper [Member] - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 979	$ 870
Average Interest Rate on Commercial Paper Borrowings	2.91%	2.25%
Parent Company [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 135	$ 136
Average Interest Rate on Commercial Paper Borrowings	4.20%	1.92%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 595	$ 320
Average Interest Rate on Commercial Paper Borrowings	2.01%	1.84%
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 0	$ 130
Average Interest Rate on Commercial Paper Borrowings	0.00%	2.38%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 0	$ 0
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 141	$ 76
Average Interest Rate on Commercial Paper Borrowings	4.45%	2.46%
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 108	$ 208
Average Interest Rate on Commercial Paper Borrowings	4.25%
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 0	$ 82
Average Interest Rate on Commercial Paper Borrowings	0.00%	2.56%
Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 54	$ 56
Average Interest Rate on Commercial Paper Borrowings	4.17%	2.02%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Outstanding Commercial Paper	$ 54	$ 70
Average Interest Rate on Commercial Paper Borrowings	4.32%	2.43%