Commitments and Contingencies - Contingencies Narrative (Details)	1 Months Ended		3 Months Ended		6 Months Ended
	Nov. 30, 2015 USD ($)	Sep. 23, 2015 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2017 USD ($) MW
Commitments And Contingencies Additional Narrative Information [Line Items]
BusinessAcquisitionResidualcommitment | MW					55
Guarantor Obligations, Maximum Exposure, Undiscounted			$ 48,000,000		$ 48,000,000
Loss Contingency, Loss in Period					0
Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Estimated Insurance Recoveries			3,200,000,000		3,200,000,000
Accrued Insurance, Current			13,400,000,000		13,400,000,000
Prepaid Reinsurance Premiums			360		360
Loss Contingency, Undiscounted Amount of Insurance-related Assessment Liability			450,000,000
Maximum liability per nuclear incident			13,000,000,000		13,000,000,000
Potomac Electric Power Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted			14,000,000		14,000,000
Baltimore Gas and Electric Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Occupancy, Net	$ 42,000,000	$ 12,000,000
Operating Leases, Income Statement, Initial Direct Costs				$ 25,000,000
Oil and Gas Property, Lease Operating Expense				29,000,000
Operating Expenses				$ 28,000,000
Nuclear Insurance Premiums [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Nuclear financial protection pool value			2,800,000,000		2,800,000,000
Nuclear Insurance Premiums [Member] | Maximum [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Nuclear financial protection pool value			$ 0		$ 0