Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Sep. 30, 2019 USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,113
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	1,507
Other Commitment, Due in Second Year	1,155
Other Commitment, Due in Third Year	52
Other Commitment, Due in Fourth Year	4
Other Commitment, Due in Fifth Year	3
Other Commitment, Due after Fifth Year	393
Guarantor Obligations, Maximum Exposure, Undiscounted	68
Letters of Credit
Other Commitments [Line Items]
Other Commitment	1,718
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	1,192
Other Commitment, Due in Second Year	515
Other Commitment, Due in Third Year	11
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Surety Bonds
Other Commitments [Line Items]
Other Commitment	991
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	315
Other Commitment, Due in Second Year	638
Other Commitment, Due in Third Year	38
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Financing trust guarantees
Other Commitments [Line Items]
Other Commitment	378
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	0
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	378
Guaranteed lease residual values
Other Commitments [Line Items]
Other Commitment	26
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	0
Other Commitment, Due in Second Year	2
Other Commitment, Due in Third Year	3
Other Commitment, Due in Fourth Year	4
Other Commitment, Due in Fifth Year	3
Other Commitment, Due after Fifth Year	15
Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Commitment	2,476
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	1,477
Other Commitment, Due in Second Year	988
Other Commitment, Due in Third Year	11
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Exelon Generation Co L L C [Member] | Letters of Credit
Other Commitments [Line Items]
Other Commitment	1,686
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	1,179
Other Commitment, Due in Second Year	496
Other Commitment, Due in Third Year	11
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Exelon Generation Co L L C [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	790
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	298
Other Commitment, Due in Second Year	492
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Other Commitment	257
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	9
Other Commitment, Due in Second Year	46
Other Commitment, Due in Third Year	2
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	200
Commonwealth Edison Co [Member] | Letters of Credit
Other Commitments [Line Items]
Other Commitment	7
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	4
Other Commitment, Due in Second Year	3
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Commonwealth Edison Co [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	50
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	5
Other Commitment, Due in Second Year	43
Other Commitment, Due in Third Year	2
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Commonwealth Edison Co [Member] | Financing trust guarantees
Other Commitments [Line Items]
Other Commitment	200
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	0
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	200
PECO Energy Co [Member]
Other Commitments [Line Items]
Other Commitment	187
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	1
Other Commitment, Due in Second Year	8
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	178
PECO Energy Co [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	9
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	1
Other Commitment, Due in Second Year	8
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
PECO Energy Co [Member] | Financing trust guarantees
Other Commitments [Line Items]
Other Commitment	178
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	0
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	178
Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	25
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	4
Other Commitment, Due in Second Year	21
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Baltimore Gas and Electric Company [Member] | Letters of Credit
Other Commitments [Line Items]
Other Commitment	8
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	2
Other Commitment, Due in Second Year	6
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Baltimore Gas and Electric Company [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	17
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	2
Other Commitment, Due in Second Year	15
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	61
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	6
Other Commitment, Due in Second Year	31
Other Commitment, Due in Third Year	3
Other Commitment, Due in Fourth Year	4
Other Commitment, Due in Fifth Year	3
Other Commitment, Due after Fifth Year	15
Guarantor Obligations, Maximum Exposure, Undiscounted	68
Pepco Holdings LLC [Member] | Letters of Credit
Other Commitments [Line Items]
Other Commitment	11
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	1
Other Commitment, Due in Second Year	10
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Pepco Holdings LLC [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	24
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	5
Other Commitment, Due in Second Year	19
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Pepco Holdings LLC [Member] | Guaranteed lease residual values
Other Commitments [Line Items]
Other Commitment	26
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	0
Other Commitment, Due in Second Year	2
Other Commitment, Due in Third Year	3
Other Commitment, Due in Fourth Year	4
Other Commitment, Due in Fifth Year	3
Other Commitment, Due after Fifth Year	15
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	36
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	2
Other Commitment, Due in Second Year	25
Other Commitment, Due in Third Year	1
Other Commitment, Due in Fourth Year	1
Other Commitment, Due in Fifth Year	1
Other Commitment, Due after Fifth Year	6
Guarantor Obligations, Maximum Exposure, Undiscounted	22
Potomac Electric Power Company [Member] | Letters of Credit
Other Commitments [Line Items]
Other Commitment	10
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	0
Other Commitment, Due in Second Year	10
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Potomac Electric Power Company [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	17
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	2
Other Commitment, Due in Second Year	15
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Potomac Electric Power Company [Member] | Guaranteed lease residual values
Other Commitments [Line Items]
Other Commitment	9
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	0
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	1
Other Commitment, Due in Fourth Year	1
Other Commitment, Due in Fifth Year	1
Other Commitment, Due after Fifth Year	6
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	16
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	3
Other Commitment, Due in Second Year	3
Other Commitment, Due in Third Year	1
Other Commitment, Due in Fourth Year	2
Other Commitment, Due in Fifth Year	1
Other Commitment, Due after Fifth Year	6
Guarantor Obligations, Maximum Exposure, Undiscounted	29
Delmarva Power and Light Company [Member] | Letters of Credit
Other Commitments [Line Items]
Other Commitment	1
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	1
Other Commitment, Due in Second Year	0
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Delmarva Power and Light Company [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	4
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	2
Other Commitment, Due in Second Year	2
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Delmarva Power and Light Company [Member] | Guaranteed lease residual values
Other Commitments [Line Items]
Other Commitment	11
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	0
Other Commitment, Due in Second Year	1
Other Commitment, Due in Third Year	1
Other Commitment, Due in Fourth Year	2
Other Commitment, Due in Fifth Year	1
Other Commitment, Due after Fifth Year	6
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	10
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	1
Other Commitment, Due in Second Year	3
Other Commitment, Due in Third Year	1
Other Commitment, Due in Fourth Year	1
Other Commitment, Due in Fifth Year	1
Other Commitment, Due after Fifth Year	3
Guarantor Obligations, Maximum Exposure, Undiscounted	17
Atlantic City Electric Company [Member] | Surety Bonds
Other Commitments [Line Items]
Other Commitment	3
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	1
Other Commitment, Due in Second Year	2
Other Commitment, Due in Third Year	0
Other Commitment, Due in Fourth Year	0
Other Commitment, Due in Fifth Year	0
Other Commitment, Due after Fifth Year	0
Atlantic City Electric Company [Member] | Guaranteed lease residual values
Other Commitments [Line Items]
Other Commitment	7
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	0
Other Commitment, Due in Second Year	1
Other Commitment, Due in Third Year	1
Other Commitment, Due in Fourth Year	1
Other Commitment, Due in Fifth Year	1
Other Commitment, Due after Fifth Year	$ 3
Maximum [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	84 years
Maximum [Member] | Guaranteed lease residual values
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	8 years
Maximum [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	33 years
Maximum [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	18 years
Maximum [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	84 years
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	24 years
Maximum [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	14 years
Maximum [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	7 years
Maximum [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	14 years
Maximum [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	3 years
Minimum [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | Guaranteed lease residual values
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	24 years
Minimum [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	1 year
Minimum [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	2 years
Minimum [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	13 years
Minimum [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Lessor, Operating Lease, Term of Contract	1 year