Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Mar. 31, 2018 USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,637
Guarantor Obligations, Maximum Exposure, Undiscounted	58
Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1,586	[1]
Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	378
Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	1,651	[2]
Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	22	[3]
Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Commitment	2,996
Exelon Generation Co L L C [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1,533	[1]
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] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	1,463	[2]
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] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	200
Commonwealth Edison Co [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	9	[2]
PECO Energy Co [Member]
Other Commitments [Line Items]
Other Commitment	188
PECO Energy Co [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1	[1]
PECO Energy Co [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	178
PECO Energy Co [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	9	[2]
Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	15
Baltimore Gas and Electric Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	5	[1]
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] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	10	[2]
PEPCO Holdings Inc [Member]
Other Commitments [Line Items]
Other Commitment	89
PEPCO Holdings Inc [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1	[1]
PEPCO Holdings Inc [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
PEPCO Holdings Inc [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	66	[2]
PEPCO Holdings Inc [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	22	[3]
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	40
Guarantor Obligations, Maximum Exposure, Undiscounted	17
Potomac Electric Power Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1	[1]
Potomac Electric Power Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Potomac Electric Power Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	32	[2]
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	24
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] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Delmarva Power and Light Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	4	[2]
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	11
Guarantor Obligations, Maximum Exposure, Undiscounted	16
Atlantic City Electric Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	0	[1]
Atlantic City Electric Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Atlantic City Electric Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	5	[2]
Atlantic City Electric Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	$ 6	[3]

[1] (a)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] (b)Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.

[3] (c)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 $58 million, $17 million of which is a guarantee by Pepco, $24 million by DPL and $16 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.