Debt and Credit Agreements - Summary of Credit Facility Thresholds (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2016
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 25
Line of Credit Facility, Current Borrowing Capacity	$ 142	$ 135
Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.275%
London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.275%
Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 25
Line of Credit Facility, Current Borrowing Capacity	$ 44	49
Exelon Generation Co L L C [Member] | Prime Rate [Member]
Line of Credit Facility [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]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.275%
Commonwealth Edison Co [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 33	33
Commonwealth Edison Co [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.075%
Commonwealth Edison Co [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.075%
PECO Energy Co [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 33	34
PECO Energy Co [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.00%
PECO Energy Co [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.90%
Baltimore Gas and Electric Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 8	5
Baltimore Gas and Electric Company [Member] | Prime Rate [Member]
Line of Credit Facility [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]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.00%
Potomac Electric Power Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 8	5
Potomac Electric Power Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.075%
Potomac Electric Power Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.075%
Delmarva Power & Light Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 8	5
Delmarva Power & Light Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.075%
Delmarva Power & Light Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.075%
Atlantic City Electric Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 8	5
Atlantic City Electric Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.075%
Atlantic City Electric Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	1.075%
Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,400
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	10,559
Revolving Credit Facility [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	5,300
Revolving Credit Facility [Member] | Commonwealth Edison Co [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,000
Revolving Credit Facility [Member] | PECO Energy Co [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600
Revolving Credit Facility [Member] | Baltimore Gas and Electric Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600
Revolving Credit Facility [Member] | Pepco Holdings LLC [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	900
Revolving Credit Facility [Member] | Potomac Electric Power Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	300
Revolving Credit Facility [Member] | Delmarva Power & Light Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	300
Revolving Credit Facility [Member] | Atlantic City Electric Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	300
Exelon Corporate [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 500
Revolving Credit Facility [Member] | Pepco Holdings LLC [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	900	$ 1,500
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600
BilateralOct2012 [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	200
BilateralJan2013 [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
BilateralJan2016 [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	150
BilateralFeb2019 [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
BilateralOct2019a [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	200
BilateralOct2019b [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
BilateralNov2019a [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	300
BilateralNov2019b [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	150
BilateralNov2019c [Member] | Line of Credit [Member] | Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 100