Debt and Credit Agreements - Commercial Paper Borrowings (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	$ 1,230
Credit facility agreements with minority and community banks	135	$ 142
Line of credit facility, remaining borrowing capacity	9,414
Commercial Paper
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	9,000	9,000
Commercial Paper	$ 1,031	$ 870
Average interest rate on commercial paper borrowings	0.25%	2.25%
Exelon Corporate [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	$ 6
Exelon Corporate [Member] | Commercial Paper
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600
Commercial Paper	0	$ 136
Average interest rate on commercial paper borrowings		1.92%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Credit facility agreements with minority and community banks	38	$ 44
Exelon Generation Co L L C [Member] | Commercial Paper
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	5,300	5,300
Commercial Paper	$ 340	$ 320
Average interest rate on commercial paper borrowings	0.27%	1.84%
Exelon Generation Co L L C [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	$ 1,500	$ 1,400
Exelon Generation Co L L C [Member] | Secured debt
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	144	159
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	2
Credit facility agreements with minority and community banks	32	33
Line of credit facility, remaining borrowing capacity	998
Commonwealth Edison Co [Member] | Commercial Paper
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	1,000	1,000
Commercial Paper	$ 323	$ 130
Average interest rate on commercial paper borrowings	0.23%	2.38%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	$ 0
Credit facility agreements with minority and community banks	33	$ 33
Line of credit facility, remaining borrowing capacity	600
PECO Energy Co [Member] | Commercial Paper
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600	600
Commercial Paper	$ 0	$ 0
Average interest rate on commercial paper borrowings	0.00%	2.39%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	$ 0
Credit facility agreements with minority and community banks	8	$ 8
Line of credit facility, remaining borrowing capacity	600
Baltimore Gas and Electric Company [Member] | Commercial Paper
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600	600
Commercial Paper	$ 0	$ 76
Average interest rate on commercial paper borrowings	0.00%	2.46%
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	$ 1
Line of credit facility, remaining borrowing capacity	899
Pepco Holdings LLC [Member] | Commercial Paper
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	900	$ 900
Commercial Paper	$ 368	208
Average interest rate on commercial paper borrowings	0.24%
Pepco Holdings LLC [Member] | Maximum [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 900
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	1
Credit facility agreements with minority and community banks	8	8
Line of credit facility, remaining borrowing capacity	299
Potomac Electric Power Company [Member] | Commercial Paper
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	300	300
Commercial Paper	$ 35	$ 82
Average interest rate on commercial paper borrowings	0.22%	2.56%
Line of credit facility, remaining borrowing capacity	$ 500
Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	0
Credit facility agreements with minority and community banks	8	$ 8
Line of credit facility, remaining borrowing capacity	300
Delmarva Power & Light Company [Member] | Commercial Paper
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	300	300
Commercial Paper	$ 146	$ 56
Average interest rate on commercial paper borrowings	0.24%	2.02%
Line of credit facility, remaining borrowing capacity	$ 500
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	0
Credit facility agreements with minority and community banks	8	$ 8
Line of credit facility, remaining borrowing capacity	300
Atlantic City Electric Company [Member] | Commercial Paper
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	300	300
Commercial Paper	$ 187	$ 70
Average interest rate on commercial paper borrowings	0.25%	2.43%
Line of credit facility, remaining borrowing capacity	$ 350