Debt and Credit Agreements - Summary of Bank Commitments, Credit Facility Borrowings and Available Capacity (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2016
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 25
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	1,443
Actual available capacity	9,116
Credit facility agreements with minority and community banks	142	$ 135
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity			$ 500
Exelon Corporate [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	6	9
Exelon Corporate [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	25
To Support Additional Commercial Paper	4,211
Credit facility agreements with minority and community banks	44	49
Exelon Generation Co L L C [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	159
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	1,400	545
Exelon Generation Co L L C [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	5
Exelon Generation Co L L C [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Actual available capacity	855
To Support Additional Commercial Paper	0
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	868
Credit facility agreements with minority and community banks	33	33
Commonwealth Edison Co [Member] | Letter of Credit [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	34
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	524
Credit facility agreements with minority and community banks	8	5
Baltimore Gas and Electric Company [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit	2
Potomac Electric Power 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	218
Credit facility agreements with minority and community banks	8	5
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	0
Actual available capacity	900
To Support Additional Commercial Paper	692
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	900	1,500
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	244
Credit facility agreements with minority and community banks	8	5
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	230
Credit facility agreements with minority and community banks	8	5
Line of Credit [Member] | Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	1,400
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	545
Line of Credit [Member] | Exelon Generation Co L L C [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	159
Long-term Line of Credit/Facility draws	0
Outstanding letters of credit	120
Actual available capacity	39
To Support Additional Commercial Paper	0
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	10,559
To Support Additional Commercial Paper	7,353
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600
To Support Additional Commercial Paper	458
Revolving Credit Facility [Member] | Exelon Generation Co L L C [Member]
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	769
Actual available capacity	4,531
Revolving Credit Facility [Member] | Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	1,000
Revolving Credit Facility [Member] | PECO Energy Co [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600
Revolving Credit Facility [Member] | Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	600
Revolving Credit Facility [Member] | Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	300
Revolving Credit Facility [Member] | Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	900
Revolving Credit Facility [Member] | Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	300
Revolving Credit Facility [Member] | Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 300
Maximum [Member] | Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 900