Commitments and Contingencies - Environmental Issues Narrative (Details)	1 Months Ended				3 Months Ended
	Aug. 31, 2015 gal	Jan. 31, 2011 gal	Jul. 31, 2010 USD ($)	Oct. 31, 2007 USD ($)	Mar. 31, 2016 USD ($) MGPSite gal Principle_responsible_party	Mar. 31, 2014 USD ($)	Sep. 30, 2013 USD ($)
Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Consent decree penalty				$ 1,000,000
Environmental loss contingencies					$ 11,000,000
PEPCO Holdings Inc [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Sites under study/remediation | MGPSite					9
Minimum estimated clean-up costs for all potentially responsible parties					$ 7,000,000
Maximum estimated clean-up costs for all potentially responsible parties					18,000,000
Environmental Remediation Expense			$ 10,000,000
Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Minimum estimated clean-up costs for all potentially responsible parties					9,000,000		$ 106,000
Maximum estimated clean-up costs for all potentially responsible parties					13,000,000		$ 161,000
QuantityOfMineralOilSPill | gal	6,100	4,500
Litigation Settlement, Expense					600,000	$ 875,000
Loss Contingency, Damages Paid, Value					250,000
Charitable donations					25,000
Potomac Electric Power Company [Member] | Minimum [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Environmental Exit Costs, Anticipated Cost					3,000,000
Potomac Electric Power Company [Member] | Maximum [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Environmental Exit Costs, Anticipated Cost					$ 6,000,000
Delmarva Power and Light Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total number of MGP sites | gal					2
Approved clean-up | MGPSite					1
Calpine Corporation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Maximum estimated clean-up costs for all potentially responsible parties					$ 10,000,000
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					50,000,000
Minimum estimated clean-up costs for all potentially responsible parties					$ 64,000,000