Debt and Credit Agreements - Summary of Bank Commitments, Credit Facility Borrowings and Available Capacity (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Long-term line of credit/facility draws	$ 0
Outstanding letters of credit	1,230
Actual available capacity	9,414
Credit facility agreements with minority and community banks	$ 135	$ 142
Minimum [Member] | Prime Rate [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.00%
Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.90%
Maximum [Member] | Prime Rate [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.275%
Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	1.275%
Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 10,644
To support additional commercial paper	7,698
Exelon Corporate [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	$ 6
Exelon Corporate [Member] | Prime Rate [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.275%
Exelon Corporate [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	1.275%
Exelon Corporate [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 600
To support additional commercial paper	594
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
To support additional commercial paper	4,698
Credit facility agreements with minority and community banks	$ 38	44
Exelon Generation Co L L C [Member] | Prime Rate [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.275%
Exelon Generation Co L L C [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	1.275%
Exelon Generation Co L L C [Member] | Secured debt
Short-term Debt [Line Items]
Outstanding letters of credit	$ 144	159
Exelon Generation Co L L C [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Outstanding letters of credit	1,500	1,400
Exelon Generation Co L L C [Member] | Line of credit
Short-term Debt [Line Items]
Actual available capacity	660
To support additional commercial paper	0
Exelon Generation Co L L C [Member] | Line of credit
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	1,500
Long-term line of credit/facility draws	0
Outstanding letters of credit	840
Exelon Generation Co L L C [Member] | Line of credit | Secured debt
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	144
Long-term line of credit/facility draws	0
Outstanding letters of credit	119
Actual available capacity	25
To support additional commercial paper	0
Exelon Generation Co L L C [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	5,300
Long-term line of credit/facility draws	0
Outstanding letters of credit	262
Actual available capacity	5,038
Exelon Generation Co L L C [Member] | Letter of credit | Community and Minority Facilities [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	5
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Long-term line of credit/facility draws	0
Outstanding letters of credit	2
Actual available capacity	998
To support additional commercial paper	675
Credit facility agreements with minority and community banks	$ 32	33
Commonwealth Edison Co [Member] | Prime Rate [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.00%
Commonwealth Edison Co [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	1.00%
Commonwealth Edison Co [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,000
Commonwealth Edison Co [Member] | Letter of credit | Community and Minority Facilities [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	5
PECO Energy Co [Member]
Short-term Debt [Line Items]
Long-term line of credit/facility draws	0
Outstanding letters of credit	0
Actual available capacity	600
To support additional commercial paper	600
Credit facility agreements with minority and community banks	$ 33	33
PECO Energy Co [Member] | Prime Rate [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.00%
PECO Energy Co [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.90%
PECO Energy Co [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 600
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Long-term line of credit/facility draws	0
Outstanding letters of credit	0
Actual available capacity	600
To support additional commercial paper	600
Credit facility agreements with minority and community banks	$ 8	8
Baltimore Gas and Electric Company [Member] | Prime Rate [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.00%
Baltimore Gas and Electric Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.90%
Baltimore Gas and Electric Company [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 600
Baltimore Gas and Electric Company [Member] | Letter of credit | Community and Minority Facilities [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	2
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Long-term line of credit/facility draws	0
Outstanding letters of credit	1
Actual available capacity	899
To support additional commercial paper	531
Pepco Holdings LLC [Member] | Revolving Credit Facility | Maximum [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	900
Pepco Holdings LLC [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]
Long-term line of credit/facility draws	0
Outstanding letters of credit	1
Actual available capacity	299
To support additional commercial paper	264
Credit facility agreements with minority and community banks	$ 8	8
Potomac Electric Power Company [Member] | Prime Rate [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.075%
Potomac Electric Power Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	1.075%
Potomac Electric Power Company [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 300
Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Long-term line of credit/facility draws	0
Outstanding letters of credit	0
Actual available capacity	300
To support additional commercial paper	154
Credit facility agreements with minority and community banks	$ 8	8
Delmarva Power & Light Company [Member] | Prime Rate [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.00%
Delmarva Power & Light Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	1.00%
Delmarva Power & Light Company [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 300
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Long-term line of credit/facility draws	0
Outstanding letters of credit	0
Actual available capacity	300
To support additional commercial paper	113
Credit facility agreements with minority and community banks	$ 8	$ 8
Atlantic City Electric Company [Member] | Prime Rate [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	0.075%
Atlantic City Electric Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end	1.075%
Atlantic City Electric Company [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 300