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Fair Value (Fair Value and Unrealized Gains and Losses for the Nuclear Decommissioning Trust Funds) (Details) - DTE Electric - Nuclear decommissioning trust fund - USD ($)
$ in Millions
Jun. 30, 2018
Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]    
Fixed income securities, fair value $ 527 $ 495
Private equity securities, fair value 10 5
Cash equivalents, fair value 9 14
Fair Value 1,484 1,492
Fixed income securities, unrealized gains 7 13
Unrealized Gains 307 333
Fixed income securities, unrealized losses (8) (3)
Unrealized Losses (51) (35)
Equity securities    
Debt Securities, Available-for-sale [Line Items]    
Fair Value 938 978
Unrealized Gains 300 320
Unrealized Losses $ (43) $ (32)