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Commitments and Contingencies (Purchase Commitments) (Details)
$ in Millions
Dec. 31, 2017
USD ($)
Purchase Obligation, Fiscal Year Maturity [Abstract]  
2018 $ 2,731
2019 1,045
2020 638
2021 474
2022 371
2023 and thereafter 2,277
Total purchase commitments 7,536
DTE Electric  
Purchase Obligation, Fiscal Year Maturity [Abstract]  
2018 930
2019 320
2020 192
2021 149
2022 88
2023 and thereafter 820
Total purchase commitments $ 2,499