Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Sep. 30, 2020 USD ($)
Other Commitments [Line Items]
Other Commitment	$ 2,924
Other Commitment, to be Paid, Remainder of Fiscal Year	612
Other Commitment, to be Paid, Year Two	1,881
Other Commitment, to be Paid, Year Three	30
Other Commitment, to be Paid, Year Four	3
Other Commitment, to be Paid, Year Five	6
Other Commitment, to be Paid, after Year Five	392
Guarantor Obligations, Maximum Exposure, Undiscounted	74
Letters of Credit
Other Commitments [Line Items]
Other Commitment	1,462
Other Commitment, to be Paid, Remainder of Fiscal Year	224
Other Commitment, to be Paid, Year Two	1,238
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Surety Bonds
Other Commitments [Line Items]
Other Commitment	1,056
Other Commitment, to be Paid, Remainder of Fiscal Year	388
Other Commitment, to be Paid, Year Two	641
Other Commitment, to be Paid, Year Three	27
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Financing trust guarantees
Other Commitments [Line Items]
Other Commitment	378
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	0
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	378
Guaranteed lease residual values
Other Commitments [Line Items]
Other Commitment	28
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	2
Other Commitment, to be Paid, Year Three	3
Other Commitment, to be Paid, Year Four	3
Other Commitment, to be Paid, Year Five	6
Other Commitment, to be Paid, after Year Five	14
Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Commitment	2,359
Other Commitment, to be Paid, Remainder of Fiscal Year	594
Other Commitment, to be Paid, Year Two	1,738
Other Commitment, to be Paid, Year Three	27
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Exelon Generation Co L L C [Member] | Letters of Credit
Other Commitments [Line Items]
Other Commitment	1,447
Other Commitment, to be Paid, Remainder of Fiscal Year	220
Other Commitment, to be Paid, Year Two	1,227
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Exelon Generation Co L L C [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	912
Other Commitment, to be Paid, Remainder of Fiscal Year	374
Other Commitment, to be Paid, Year Two	511
Other Commitment, to be Paid, Year Three	27
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Other Commitment	223
Other Commitment, to be Paid, Remainder of Fiscal Year	5
Other Commitment, to be Paid, Year Two	18
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	200
Commonwealth Edison Co [Member] | Letters of Credit
Other Commitments [Line Items]
Other Commitment	7
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	7
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Commonwealth Edison Co [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	16
Other Commitment, to be Paid, Remainder of Fiscal Year	5
Other Commitment, to be Paid, Year Two	11
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Commonwealth Edison Co [Member] | Financing trust guarantees
Other Commitments [Line Items]
Other Commitment	200
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	0
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	200
PECO Energy Co [Member]
Other Commitments [Line Items]
Other Commitment	180
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	2
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	178
PECO Energy Co [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	2
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	2
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
PECO Energy Co [Member] | Financing trust guarantees
Other Commitments [Line Items]
Other Commitment	178
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	0
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	178
Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	5
Other Commitment, to be Paid, Remainder of Fiscal Year	3
Other Commitment, to be Paid, Year Two	2
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Baltimore Gas and Electric Company [Member] | Letters of Credit
Other Commitments [Line Items]
Other Commitment	2
Other Commitment, to be Paid, Remainder of Fiscal Year	2
Other Commitment, to be Paid, Year Two	0
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Baltimore Gas and Electric Company [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	3
Other Commitment, to be Paid, Remainder of Fiscal Year	1
Other Commitment, to be Paid, Year Two	2
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	49
Other Commitment, to be Paid, Remainder of Fiscal Year	3
Other Commitment, to be Paid, Year Two	20
Other Commitment, to be Paid, Year Three	3
Other Commitment, to be Paid, Year Four	3
Other Commitment, to be Paid, Year Five	6
Other Commitment, to be Paid, after Year Five	14
Guarantor Obligations, Maximum Exposure, Undiscounted	74
Pepco Holdings LLC [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	21
Other Commitment, to be Paid, Remainder of Fiscal Year	3
Other Commitment, to be Paid, Year Two	18
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Pepco Holdings LLC [Member] | Guaranteed lease residual values
Other Commitments [Line Items]
Other Commitment	28
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	2
Other Commitment, to be Paid, Year Three	3
Other Commitment, to be Paid, Year Four	3
Other Commitment, to be Paid, Year Five	6
Other Commitment, to be Paid, after Year Five	14
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	23
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	14
Other Commitment, to be Paid, Year Three	1
Other Commitment, to be Paid, Year Four	1
Other Commitment, to be Paid, Year Five	2
Other Commitment, to be Paid, after Year Five	5
Guarantor Obligations, Maximum Exposure, Undiscounted	25
Potomac Electric Power Company [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	14
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	14
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Potomac Electric Power Company [Member] | Guaranteed lease residual values
Other Commitments [Line Items]
Other Commitment	9
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	0
Other Commitment, to be Paid, Year Three	1
Other Commitment, to be Paid, Year Four	1
Other Commitment, to be Paid, Year Five	2
Other Commitment, to be Paid, after Year Five	5
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	16
Other Commitment, to be Paid, Remainder of Fiscal Year	2
Other Commitment, to be Paid, Year Two	3
Other Commitment, to be Paid, Year Three	1
Other Commitment, to be Paid, Year Four	1
Other Commitment, to be Paid, Year Five	3
Other Commitment, to be Paid, after Year Five	6
Guarantor Obligations, Maximum Exposure, Undiscounted	31
Delmarva Power and Light Company [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	4
Other Commitment, to be Paid, Remainder of Fiscal Year	2
Other Commitment, to be Paid, Year Two	2
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Delmarva Power and Light Company [Member] | Guaranteed lease residual values
Other Commitments [Line Items]
Other Commitment	12
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	1
Other Commitment, to be Paid, Year Three	1
Other Commitment, to be Paid, Year Four	1
Other Commitment, to be Paid, Year Five	3
Other Commitment, to be Paid, after Year Five	6
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	10
Other Commitment, to be Paid, Remainder of Fiscal Year	1
Other Commitment, to be Paid, Year Two	3
Other Commitment, to be Paid, Year Three	1
Other Commitment, to be Paid, Year Four	1
Other Commitment, to be Paid, Year Five	1
Other Commitment, to be Paid, after Year Five	3
Guarantor Obligations, Maximum Exposure, Undiscounted	18
Atlantic City Electric Company [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	3
Other Commitment, to be Paid, Remainder of Fiscal Year	1
Other Commitment, to be Paid, Year Two	2
Other Commitment, to be Paid, Year Three	0
Other Commitment, to be Paid, Year Four	0
Other Commitment, to be Paid, Year Five	0
Other Commitment, to be Paid, after Year Five	0
Atlantic City Electric Company [Member] | Guaranteed lease residual values
Other Commitments [Line Items]
Other Commitment	7
Other Commitment, to be Paid, Remainder of Fiscal Year	0
Other Commitment, to be Paid, Year Two	1
Other Commitment, to be Paid, Year Three	1
Other Commitment, to be Paid, Year Four	1
Other Commitment, to be Paid, Year Five	1
Other Commitment, to be Paid, after Year Five	$ 3
Maximum [Member] | Guaranteed lease residual values
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	8 years
Minimum [Member] | Guaranteed lease residual values
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	1 year