Impairment of Long-Lived Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Estimated residual value of leased assets	$ 356
Proceeds From Lease Termination	360	$ 0
Gain (Loss) on Contract Termination	4
Operating and maintenance	2,835	$ 2,081
Assets	111,742		$ 95,384
Constellation Energy Group LLC [Member]
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Tangible Asset Impairment Charges	119
Assets	$ 63