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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, 2019
Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]    
Fair Value $ 1,577 $ 1,378
Fixed income securities, fair value 544 502
Private equity and other, fair value 34 20
Cash equivalents, fair value 9 5
Unrealized Gains 362 242
Fixed income securities, unrealized gains 27 7
Unrealized Losses (54) (87)
Fixed income securities, unrealized losses (1) (8)
Equity securities    
Debt Securities, Available-for-sale [Line Items]    
Fair Value 990 851
Unrealized Gains 335 235
Unrealized Losses $ (53) $ (79)