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Property, Plant, and Equipment (Capital Leases) (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Capital Leased Assets [Line Items]    
Gross property under capital leases $ 44 $ 44
Accumulated amortization of property under capital leases 38 32
DTE Electric    
Capital Leased Assets [Line Items]    
Gross property under capital leases 18 18
Accumulated amortization of property under capital leases $ 12 $ 6