Commitments and Contingencies - Schedule of Future Rental Expense under Operating Leases (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense	$ 865		$ 806		$ 930
Exelon Generation Co L L C [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense	806	[1]	744	[1]	872	[1]
Long Term Contract For Purchase Of Electric Power Capacity	755		694		801
Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense	15		15		18
PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense	14		21		27
Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense	$ 12		$ 11		$ 12

[1] Includes Generation’s PPAs and other capacity contracts that are accounted for as operating leases and are reflected as net capacity purchases in the Energy Commitments table above. These agreements are considered contingent operating lease payments and are not included in the minimum future operating lease payments table above. Payments made under Generation’s PPAs and other capacity contracts totaled $755 million, $694 million and $801 million during 2014, 2013 and 2012, respectively.