Commitments and Contingencies - Environmental Issues Narrative (Details) $ in Millions	1 Months Ended		3 Months Ended	9 Months Ended
	Jan. 31, 2015 USD ($)	Oct. 31, 2007 USD ($)	Sep. 30, 2015 USD ($) MGPSite	Sep. 30, 2015 USD ($) MGPSite Principle_responsible_party	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)
Accrual For Environmental Loss Contingencies [Line Items]
Net investment in long-term direct financing leases			$ 348.0	$ 348.0	$ 361.0
Litigation Settlement, Amount	$ 14.0
Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total number of MGP sites | MGPSite			42	42
Approved clean-up | MGPSite			17	17
Sites under study/remediation | MGPSite			25	25
Other Increase (Decrease) in Environmental Liabilities			$ 50.0
PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total number of MGP sites | MGPSite			26	26
Approved clean-up | MGPSite			16	16
Sites under study/remediation | MGPSite			10	10
Other Increase (Decrease) in Environmental Liabilities			$ 1.0
Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total number of MGP sites | MGPSite			13	13
Sites under study/remediation | MGPSite			2	2
Loss Contingency, Estimate of Possible Loss			$ 1.7	$ 1.7
Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Consent decree penalty		$ 1.0
Environmental loss contingencies			12.0	12.0	$ 13.0
Loss Contingency, Estimate of Possible Loss						$ 105.0
Cotter Corporation [Member] | Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total cost of remediation to be shared by PRPs				60.0
DOJ potential settlement				$ 90.0
Sixty-Eighth Street Dump [Member] | Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Loss Contingency Number Of Parties Jointly And Severally Liable In Environmental Protection Agency Action | Principle_responsible_party				19
Minimum estimated clean-up costs for all potentially responsible parties			50.0	$ 50.0
Maximum estimated clean-up costs for all potentially responsible parties			64.0	64.0
Rossville ash site [Member] | Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss			$ 9.0	$ 9.0