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Impairment of Long-Lived Assets (Details) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended
Sep. 30, 2016
Mar. 31, 2017
Mar. 31, 2016
Capital Leases, Net Investment in Direct Financing Leases [Abstract]      
Proceeds from Long-term Capital Lease Obligations     $ 360
Estimated residual value of leased assets     356
Proceeds From Lease Termination   $ 0 360
Gain (Loss) on Contract Termination     4
Constellation Energy Group LLC [Member]      
Capital Leases, Net Investment in Direct Financing Leases [Abstract]      
Tangible Asset Impairment Charges $ 15   $ 119