Debt and Credit Agreements - Summary of Outstanding Long-term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term debt, gross	$ 36,516	$ 35,560
Unamortized debt discount and premium, net	(77)	(72)
Unamortized debt issuance costs	(248)	(214)
Fair value adjustment	721	765
Long-term Debt, Current Maturities	(1,819)	(4,710)
Long-term debt to financing trusts	390	390
Secured debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 18,915	17,486
Secured debt | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.19%
Secured debt | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.90%
Senior unsecured notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 10,585	10,685
Senior unsecured notes | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.45%
Senior unsecured notes | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.60%
Unsecured notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 3,700	3,300
Unsecured notes | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.40%
Unsecured notes | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.35%
Pollution control notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 0	412
Pollution control notes | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.50%
Pollution control notes | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.70%
Nuclear fuel procurement contracts
Debt Instrument [Line Items]
Long-term debt, gross	$ 0	3
Nuclear fuel procurement contracts | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.15%
Notes payable and other
Debt Instrument [Line Items]
Long-term debt, gross	$ 170	154
Notes payable and other | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.10%
Notes payable and other | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.99%
Junior subordinated notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,150	1,150
Junior subordinated notes | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.50%
Long-term software licensing agreement
Debt Instrument [Line Items]
Long-term debt, gross	$ 30	55
Long-term software licensing agreement | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.95%
Unsecured tax-exempt bonds
Debt Instrument [Line Items]
Long-term debt, gross	$ 143	222
Unsecured tax-exempt bonds | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.17%
Unsecured tax-exempt bonds | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.70%
Medium-term notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 10	10
Medium-term notes | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage
Medium-term notes | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.72%
Transition bonds
Debt Instrument [Line Items]
Long-term debt, gross	$ 21	40
Transition bonds | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.55%
Loan agreement
Debt Instrument [Line Items]
Long-term debt, gross	$ 50	50
Loan agreement | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.00%
Fixed rates
Debt Instrument [Line Items]
Long-term debt, gross	$ 977	1,182
Fixed rates | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.29%
Fixed rates | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.00%
Variable rates
Debt Instrument [Line Items]
Long-term debt, gross	$ 765	811
Variable rates | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.99%
Variable rates | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.18%
Long-term debt to financing trusts
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 390	390
ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 206	206
ComEd Financing III Affiliate [Member] | Long-term debt to financing trusts
Debt Instrument [Line Items]
Long-term debt to financing trusts		206
ComEd Financing III Affiliate [Member] | Long-term debt to financing trusts | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.35%
PECO Trust III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 81	81
PECO Trust III Affiliate [Member] | Long-term debt to financing trusts
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 81	81
PECO Trust III Affiliate [Member] | Long-term debt to financing trusts | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.25%
PECO Trust III Affiliate [Member] | Long-term debt to financing trusts | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.38%
PECO Trust IV Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 103	103
PECO Trust IV Affiliate [Member] | Long-term debt to financing trusts
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 103	103
PECO Trust IV Affiliate [Member] | Long-term debt to financing trusts | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.75%
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 6,072	7,943
Unamortized debt discount and premium, net	(5)	(5)
Unamortized debt issuance costs	(46)	(42)
Fair value adjustment	66	78
Long-term Debt, Current Maturities	(197)	(3,182)
Long-term debt	5,890	4,792
Exelon Generation Co L L C [Member] | Senior unsecured notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 4,219	5,420
Exelon Generation Co L L C [Member] | Senior unsecured notes | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.25%
Exelon Generation Co L L C [Member] | Senior unsecured notes | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.60%
Exelon Generation Co L L C [Member] | Pollution control notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 0	412
Exelon Generation Co L L C [Member] | Pollution control notes | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.50%
Exelon Generation Co L L C [Member] | Pollution control notes | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.70%
Exelon Generation Co L L C [Member] | Nuclear fuel procurement contracts
Debt Instrument [Line Items]
Long-term debt, gross	$ 0	3
Exelon Generation Co L L C [Member] | Nuclear fuel procurement contracts | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.15%
Exelon Generation Co L L C [Member] | Notes payable and other
Debt Instrument [Line Items]
Long-term debt, gross	$ 111	115
Exelon Generation Co L L C [Member] | Notes payable and other | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.10%
Exelon Generation Co L L C [Member] | Notes payable and other | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.85%
Exelon Generation Co L L C [Member] | Fixed rates
Debt Instrument [Line Items]
Long-term debt, gross	$ 977	1,182
Exelon Generation Co L L C [Member] | Fixed rates | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.29%
Exelon Generation Co L L C [Member] | Fixed rates | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.00%
Exelon Generation Co L L C [Member] | Variable rates
Debt Instrument [Line Items]
Long-term debt, gross	$ 765	811
Exelon Generation Co L L C [Member] | Variable rates | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.99%
Exelon Generation Co L L C [Member] | Variable rates | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.18%
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 9,087	8,586
Unamortized debt discount and premium, net	(28)	(27)
Unamortized debt issuance costs	(76)	(68)
Long-term Debt, Current Maturities	(350)	(500)
Long-term debt to financing trusts	205	205
Commonwealth Edison Co [Member] | Secured debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 9,079	8,578
Commonwealth Edison Co [Member] | Secured debt | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.20%
Commonwealth Edison Co [Member] | Secured debt | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.45%
Commonwealth Edison Co [Member] | Notes payable and other
Debt Instrument [Line Items]
Finance lease, liability	$ 8	8
Commonwealth Edison Co [Member] | Notes payable and other | Maximum [Member]
Debt Instrument [Line Items]
Lessee, finance lease, discount rate	7.49%
Commonwealth Edison Co [Member] | Long-term debt to financing trusts
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 206	206
Commonwealth Edison Co [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs	(1)	(1)
Long-term debt to financing trusts	205	205
Commonwealth Edison Co [Member] | ComEd Financing III Affiliate [Member] | Long-term debt to financing trusts
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 206	206
Commonwealth Edison Co [Member] | ComEd Financing III Affiliate [Member] | Long-term debt to financing trusts | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.35%
Commonwealth Edison Co [Member] | PECO Trust III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 0	0
Commonwealth Edison Co [Member] | PECO Trust IV Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	0	0
PECO Energy Co [Member]
Debt Instrument [Line Items]
Long-term debt, gross	3,800	3,450
Unamortized debt discount and premium, net	(20)	(21)
Unamortized debt issuance costs	(27)	(24)
Long-term Debt, Current Maturities	(300)	0
Long-term debt to financing trusts	184	184
PECO Energy Co [Member] | Secured debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 3,750	3,400
PECO Energy Co [Member] | Secured debt | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.70%
PECO Energy Co [Member] | Secured debt | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.95%
PECO Energy Co [Member] | Loan agreement
Debt Instrument [Line Items]
Long-term debt, gross	$ 50	50
PECO Energy Co [Member] | Loan agreement | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.00%
PECO Energy Co [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 0	0
PECO Energy Co [Member] | PECO Trust III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	81	81
PECO Energy Co [Member] | PECO Trust III Affiliate [Member] | Long-term debt to financing trusts
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 81	81
PECO Energy Co [Member] | PECO Trust III Affiliate [Member] | Long-term debt to financing trusts | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.25%
PECO Energy Co [Member] | PECO Trust III Affiliate [Member] | Long-term debt to financing trusts | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.38%
PECO Energy Co [Member] | PECO Trust IV Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 103	103
PECO Energy Co [Member] | PECO Trust IV Affiliate [Member] | Long-term debt to financing trusts
Debt Instrument [Line Items]
Long-term debt to financing trusts	$ 103	103
PECO Energy Co [Member] | PECO Trust IV Affiliate [Member] | Long-term debt to financing trusts | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.75%
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 3,700	3,300
Unamortized debt discount and premium, net	(12)	(9)
Unamortized debt issuance costs	(24)	(21)
Long-term Debt, Current Maturities	(300)	0
Baltimore Gas and Electric Company [Member] | Senior unsecured notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 3,700	3,300
Baltimore Gas and Electric Company [Member] | Senior unsecured notes | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.40%
Baltimore Gas and Electric Company [Member] | Senior unsecured notes | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.35%
Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 6,496	5,995
Finance lease, liability	50
Unamortized debt discount and premium, net	4	4
Unamortized debt issuance costs	(28)	(19)
Fair value adjustment	534	583
Long-term debt due within one year	(347)	(103)
Pepco Holdings LLC [Member] | Secured debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 6,086	5,508
Pepco Holdings LLC [Member] | Secured debt | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.19%
Pepco Holdings LLC [Member] | Secured debt | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.90%
Pepco Holdings LLC [Member] | Unsecured notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 185	185
Pepco Holdings LLC [Member] | Unsecured notes | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.45%
Pepco Holdings LLC [Member] | Notes payable and other
Debt Instrument [Line Items]
Long-term debt, gross	$ 1	2
Finance lease, liability	$ 50	28
Pepco Holdings LLC [Member] | Notes payable and other | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.28%
Pepco Holdings LLC [Member] | Notes payable and other | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.99%
Lessee, finance lease, discount rate	3.54%
Pepco Holdings LLC [Member] | Unsecured tax-exempt bonds
Debt Instrument [Line Items]
Long-term debt, gross	$ 143	222
Pepco Holdings LLC [Member] | Unsecured tax-exempt bonds | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.17%
Pepco Holdings LLC [Member] | Unsecured tax-exempt bonds | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.70%
Pepco Holdings LLC [Member] | Medium-term notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 10	10
Pepco Holdings LLC [Member] | Medium-term notes | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.72%
Pepco Holdings LLC [Member] | Transition bonds
Debt Instrument [Line Items]
Long-term debt, gross	$ 21	40
Pepco Holdings LLC [Member] | Transition bonds | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.55%
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 3,203	2,897
Finance lease, liability	17
Unamortized debt discount and premium, net	2	2
Unamortized debt issuance costs	(40)	(35)
Long-term debt due within one year	(3)	(2)
Potomac Electric Power Company [Member] | Secured debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 3,075	2,775
Potomac Electric Power Company [Member] | Secured debt | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.53%
Potomac Electric Power Company [Member] | Secured debt | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.90%
Potomac Electric Power Company [Member] | Notes payable and other
Debt Instrument [Line Items]
Long-term debt, gross	$ 1	2
Finance lease, liability	$ 17	10
Potomac Electric Power Company [Member] | Notes payable and other | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.28%
Potomac Electric Power Company [Member] | Notes payable and other | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.99%
Lessee, finance lease, discount rate	3.54%
Potomac Electric Power Company [Member] | Unsecured tax-exempt bonds
Debt Instrument [Line Items]
Long-term debt, gross	$ 110	110
Potomac Electric Power Company [Member] | Unsecured tax-exempt bonds | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.70%
Delmarva Power & Light Company [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,687	1,578
Finance lease, liability	20
Unamortized debt discount and premium, net	1	1
Unamortized debt issuance costs	(11)	(12)
Long-term Debt, Current Maturities	79	79
Long-term debt due within one year	(82)	(80)
Delmarva Power & Light Company [Member] | Secured debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,624	1,446
Delmarva Power & Light Company [Member] | Secured debt | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.19%
Delmarva Power & Light Company [Member] | Secured debt | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	4.27%
Delmarva Power & Light Company [Member] | Notes payable and other
Debt Instrument [Line Items]
Finance lease, liability	$ 20	10
Delmarva Power & Light Company [Member] | Notes payable and other | Maximum [Member]
Debt Instrument [Line Items]
Lessee, finance lease, discount rate	3.54%
Delmarva Power & Light Company [Member] | Unsecured tax-exempt bonds
Debt Instrument [Line Items]
Long-term debt, gross	$ 33	112
Delmarva Power & Light Company [Member] | Unsecured tax-exempt bonds | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.17%
Delmarva Power & Light Company [Member] | Unsecured tax-exempt bonds | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.20%
Delmarva Power & Light Company [Member] | Medium-term notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 10	10
Delmarva Power & Light Company [Member] | Medium-term notes | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.72%
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,421	1,335
Finance lease, liability	13
Unamortized debt discount and premium, net	(1)	(1)
Unamortized debt issuance costs	(7)	(7)
Long-term debt due within one year	(261)	(20)
Atlantic City Electric Company [Member] | Secured debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,387	1,287
Atlantic City Electric Company [Member] | Secured debt | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.25%
Atlantic City Electric Company [Member] | Secured debt | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.80%
Atlantic City Electric Company [Member] | Notes payable and other
Debt Instrument [Line Items]
Finance lease, liability	$ 13	8
Atlantic City Electric Company [Member] | Notes payable and other | Maximum [Member]
Debt Instrument [Line Items]
Lessee, finance lease, discount rate	3.54%
Atlantic City Electric Company [Member] | Transition bonds
Debt Instrument [Line Items]
Long-term debt, gross	$ 21	$ 40
Atlantic City Electric Company [Member] | Transition bonds | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.55%