Commitments and Contingencies - Contingencies Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) MW
Commitments And Contingencies Additional Narrative Information [Line Items]
BusinessAcquisitionResidualcommitment | MW	55
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 48
Loss Contingency, Loss in Period	0
Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Required nuclear liability insurance per site	0
Loss Contingency, Undiscounted Amount of Insurance-related Assessment Liability	450
Current Liability Per Incident	13,400
Maximum liability per nuclear incident	13,000
Mutual Replacement Power Cost Insurance Maximum Retrospective Premium Obligation	3,200
Potomac Electric Power Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	14
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
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