Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Sep. 30, 2018 USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,386
Guarantor Obligations, Maximum Exposure, Undiscounted	60
Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1,584	[1]
Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	1,402	[2]
Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	378
Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	22	[3]
Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Commitment	2,766
Exelon Generation Co L L C [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1,565	[1]
Exelon Generation Co L L C [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	1,201	[2]
Exelon Generation Co L L C [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Exelon Generation Co L L C [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	0	[3]
Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Other Commitment	211
Commonwealth Edison Co [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	2	[1]
Commonwealth Edison Co [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	9	[2]
Commonwealth Edison Co [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	200
Commonwealth Edison Co [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	0	[3]
PECO Energy Co [Member]
Other Commitments [Line Items]
Other Commitment	187
PECO Energy Co [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	0	[1]
PECO Energy Co [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	9	[2]
PECO Energy Co [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	178
PECO Energy Co [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	0	[3]
Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	28
Baltimore Gas and Electric Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	3	[1]
Baltimore Gas and Electric Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	25	[2]
Baltimore Gas and Electric Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Baltimore Gas and Electric Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	0	[3]
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	91
Pepco Holdings LLC [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	4	[1]
Pepco Holdings LLC [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	65	[2]
Pepco Holdings LLC [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	22	[3]
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	43
Guarantor Obligations, Maximum Exposure, Undiscounted	17
Potomac Electric Power Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	4	[1]
Potomac Electric Power Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	32	[2]
Potomac Electric Power Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Potomac Electric Power Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	7	[3]
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	13
Guarantor Obligations, Maximum Exposure, Undiscounted	25
Delmarva Power and Light Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	0	[1]
Delmarva Power and Light Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	4	[2]
Delmarva Power and Light Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Delmarva Power and Light Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	9	[3]
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	9
Guarantor Obligations, Maximum Exposure, Undiscounted	17
Atlantic City Electric Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	0	[1]
Atlantic City Electric Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	3	[2]
Atlantic City Electric Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Atlantic City Electric Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	$ 6	[3]

[1] Letters of credit (non-debt) - Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties.

[2] Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.

[3] Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $60 million, $17 million of which is a guarantee by Pepco, $25 million by DPL and $17 million by ACE. The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote.