Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at Amortized Cost (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust	$ 390	$ 390
Spent Nuclear Fuel Obligation, Noncurrent	1,208	1,208
Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	38,529	36,912
Long-term debt to financing trust	390	390
Spent Nuclear Fuel Obligation, Noncurrent	1,208	1,208
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	42,370	43,752
Long-term debt to financing trust	465	467
Spent Nuclear Fuel Obligation, Noncurrent	979	909
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Long-term debt to financing trust	0	0
Spent Nuclear Fuel Obligation, Noncurrent	0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	39,255	40,688
Long-term debt to financing trust	0	0
Spent Nuclear Fuel Obligation, Noncurrent	979	909
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	3,115	3,064
Long-term debt to financing trust	465	467
Spent Nuclear Fuel Obligation, Noncurrent	0	0
Exelon Generation Co L L C [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Spent Nuclear Fuel Obligation, Noncurrent	1,208	1,208
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	6,060	6,087
Spent Nuclear Fuel Obligation, Noncurrent	1,208	1,208
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	6,655	6,856
Spent Nuclear Fuel Obligation, Noncurrent	979	909
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Spent Nuclear Fuel Obligation, Noncurrent	0	0
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	5,497	5,648
Spent Nuclear Fuel Obligation, Noncurrent	979	909
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	1,158	1,208
Spent Nuclear Fuel Obligation, Noncurrent	0	0
Commonwealth Edison Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust	205	205
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	9,674	8,983
Long-term debt to financing trust	205	205
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	10,853	11,117
Long-term debt to financing trust	243	246
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Long-term debt to financing trust	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	10,853	11,117
Long-term debt to financing trust	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Long-term debt to financing trust	243	246
PECO Energy Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust	184	184
PECO Energy Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	4,125	3,753
Long-term debt to financing trust	184	184
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	4,541	4,603
Long-term debt to financing trust	222	221
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Long-term debt to financing trust	0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	4,491	4,553
Long-term debt to financing trust	0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	50	50
Long-term debt to financing trust	222	221
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	3,665	3,664
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	3,991	4,366
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	3,991	4,366
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Pepco Holdings LLC [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	7,577	7,006
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	7,957	7,905
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	6,050	6,099
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	1,907	1,806
Potomac Electric Power Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	3,317	3,165
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	3,935	4,084
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	3,112	3,336
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	823	748
Delmarva Power and Light Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	1,802	1,677
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	1,910	1,939
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	1,386	1,484
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	524	455
Atlantic City Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	1,718	1,413
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	1,862	1,620
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	1,302	1,018
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	$ 560	$ 602