Debt and Credit Agreements - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) MW	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	$ (1,819)	$ (4,710)
Debt Instrument, Collateral Amount	2,200
Long-term line of credit/facility draws	0
Letters of Credit Outstanding, Amount	1,230
Long-term Debt	36,906
Long-term debt, gross	$ 36,516	35,560
Maximum [Member]
Debt Instrument [Line Items]
Basis Points For Prime Based Borrowings	0.65%
Basis Points For Libor Based Borrowings	1.65%
DOE Project Financing, 2.82% January 5, 2037 [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Long-term line of credit/facility draws	$ 646
Debt, Weighted Average Interest Rate	2.82%
Non-recourse debt	$ 460	485
Letters of Credit Outstanding, Amount	$ 37
Debt Instrument, Basis Spread on Variable Rate	0.375%
Renewable Power Generation [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Non-recourse debt	$ 95	106
Debt Instrument, Face Amount	$ 150
Debt instrument, interest rate, stated percentage	4.11%
SolGen [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Non-recourse debt	$ 125	$ 131
Debt Instrument, Face Amount	$ 150
Debt instrument, interest rate, stated percentage	3.93%
ExGenRenewablesIVNov2024 [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Non-recourse debt	$ 709
Long-term Debt	850
Non Recourse Debt Interest Rate Swap	636
Non Recourse Debt Hedge Percentage		2.32%
Continetal Wind [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	122
Non-recourse debt	415	$ 447
Letters of Credit Outstanding, Amount	114
Debt Instrument, Face Amount	$ 613
Non Recourse Debt Megawatts | MW	667
Debt instrument, interest rate, stated percentage	6.00%
Aggregate Bank Commitments Under Unsecured Revolving Credit Facilities	$ 4
ExGenRenewablesIVDec2020 [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.75%
Long-term Debt	$ 750
Non Recourse Debt Interest Rate Swap	$ 516
Non Recourse Debt Hedge Percentage	1.05%
Non Recourse Debt Minimum Rate	1.00%
Long-term debt, gross	$ 750
Corporate, Non-Segment [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.65%	0.95%
Exelon Corporate [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	$ 6
Long-term Debt	7,589
Long-term debt, gross	7,589	$ 7,039
Exelon Corporate [Member] | Corporate, Non-Segment [Member]
Debt Instrument [Line Items]
Short-Term Loan Agreements	500
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	(197)	(3,182)
Debt Instrument, Collateral Amount	2,200
Long-term Debt	6,072
Long-term debt, gross	6,072	7,943
Exelon Generation Co L L C [Member] | ShortTermDebt03192020 [Member]
Debt Instrument [Line Items]
Short-Term Loan Agreements	$ 200
Exelon Generation Co L L C [Member] | ShortTermDebt03192020 [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.50%
Exelon Generation Co L L C [Member] | ShortTermDebt03312020 [Member]
Debt Instrument [Line Items]
Short-Term Loan Agreements	$ 300
Exelon Generation Co L L C [Member] | ShortTermDebt03312020 [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.75%
Exelon Generation Co L L C [Member] | DOE Project Financing, 2.82% January 5, 2037 [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Long-term line of credit/facility draws	$ 646
Debt, Weighted Average Interest Rate	2.82%
Non-recourse debt	$ 460	485
Letters of Credit Outstanding, Amount	$ 37
Debt Instrument, Basis Spread on Variable Rate	0.375%
Exelon Generation Co L L C [Member] | Renewable Power Generation [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Non-recourse debt	$ 95	106
Debt Instrument, Face Amount	$ 150
Debt instrument, interest rate, stated percentage	4.11%
Exelon Generation Co L L C [Member] | SolGen [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Non-recourse debt	$ 125	$ 131
Debt Instrument, Face Amount	$ 150
Debt instrument, interest rate, stated percentage	3.93%
Exelon Generation Co L L C [Member] | ExGenRenewablesIVNov2024 [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Non-recourse debt	$ 709
Long-term Debt	850
Non Recourse Debt Interest Rate Swap	636
Non Recourse Debt Hedge Percentage		2.32%
Exelon Generation Co L L C [Member] | Continetal Wind [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	122
Non-recourse debt	415	$ 447
Letters of Credit Outstanding, Amount	114
Debt Instrument, Face Amount	$ 613
Non Recourse Debt Megawatts | MW	667
Debt instrument, interest rate, stated percentage	6.00%
Aggregate Bank Commitments Under Unsecured Revolving Credit Facilities	$ 4
Exelon Generation Co L L C [Member] | ExGenRenewablesIVDec2020 [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.75%
Long-term Debt	$ 750
Non Recourse Debt Interest Rate Swap	$ 516
Non Recourse Debt Hedge Percentage	1.05%
Non Recourse Debt Minimum Rate	1.00%
Long-term debt, gross	$ 750
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	(350)	(500)
Long-term line of credit/facility draws	0
Letters of Credit Outstanding, Amount	2
Long-term Debt	9,292
Long-term debt, gross	9,087	8,586
Commonwealth Edison Co [Member] | ShortTermDebt752021 [Member]
Debt Instrument [Line Items]
Short-Term Loan Agreements	125
Commonwealth Edison Co [Member] | ShortTermDebt502021 [Member]
Debt Instrument [Line Items]
Short-Term Loan Agreements	$ 125
Commonwealth Edison Co [Member] | ShortTermDebt502021 [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.50%
Delmarva Power & Light Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	$ 79	79
Long-term line of credit/facility draws	0
Letters of Credit Outstanding, Amount	0
Long-term Debt	1,687
Long-term debt, gross	1,687	$ 1,578
Exelon Corporate [Member] | Corporate, Non-Segment [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	550
Revolving Credit Facility
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	10,644
Revolving Credit Facility | Exelon Corporate [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600
Revolving Credit Facility | Exelon Corporate [Member] | Corporate, Non-Segment [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	550
Revolving Credit Facility | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value of amount outstanding	1,500
Line of Credit Facility, Maximum Borrowing Capacity	5,300
Long-term line of credit/facility draws	0
Letters of Credit Outstanding, Amount	262
Revolving Credit Facility | Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,000
Revolving Credit Facility | Delmarva Power & Light Company [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 300
Line of credit | Corporate, Non-Segment [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.75%
Line of credit | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,500
Long-term line of credit/facility draws	0
Letters of Credit Outstanding, Amount	$ 840
Line of credit | Commonwealth Edison Co [Member] | ShortTermDebt752021 [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.75%