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Fair Value (Fair Value and Unrealized Gains and Losses for the Nuclear Decommissioning Trust Funds) (Details) - DTE Electric - USD ($)
$ in Millions
Jun. 30, 2021
Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]    
Fair Value $ 2,019 $ 1,855
Unrealized Gains 596 501
Unrealized Losses (7) (7)
Cash equivalents    
Debt Securities, Available-for-sale [Line Items]    
Fair Value 34 27
Private equity and other    
Debt Securities, Available-for-sale [Line Items]    
Fair Value 159 104
Unrealized Gains 26 0
Unrealized Losses 0 0
Equity securities    
Debt Securities, Available-for-sale [Line Items]    
Fair Value 1,168 1,169
Unrealized Gains 546 481
Unrealized Losses (4) (6)
Fixed income securities    
Debt Securities, Available-for-sale [Line Items]    
Fair Value 658 555
Unrealized Gains 24 20
Unrealized Losses $ (3) $ (1)