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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
Sep. 30, 2020
Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]    
Fair Value $ 1,664 $ 1,661
Fixed income securities, fair value 527 538
Private equity and other, fair value 78 43
Cash equivalents, fair value 46 34
Unrealized Gains 341 420
Fixed income securities, unrealized gains 16 24
Unrealized Losses (29) (40)
Fixed income securities, unrealized losses (1) (1)
Equity securities    
Debt Securities, Available-for-sale [Line Items]    
Fair Value 1,013 1,046
Unrealized Gains 325 396
Unrealized Losses $ (28) $ (39)