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Fair Value (Fair Value and Unrealized Gains and Losses for the Nuclear Decommissioning Trust Funds) (Details) - DTE Electric - Nuclear decommissioning trusts - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]    
Fair Value $ 1,661 $ 1,378
Fixed income securities, fair value 538 502
Private equity and other, fair value 43 20
Cash equivalents, fair value 34 5
Unrealized gains 420 242
Fixed income securities, unrealized gains 24 7
Unrealized losses (40) (87)
Fixed income securities, unrealized losses (1) (8)
Equity securities    
Debt Securities, Available-for-sale [Line Items]    
Fair Value 1,046 851
Unrealized gains 396 235
Unrealized losses $ (39) $ (79)