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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, 2018
Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]    
Fair Value $ 1,378 $ 1,492
Fixed income securities, fair value 502 495
Private equity securities, fair value 20 5
Cash equivalents, fair value 5 14
Unrealized gains 242 333
Fixed income securities, unrealized gain 7 13
Unrealized losses (87) (35)
Fixed income securities, unrealized loss (8) (3)
Equity securities    
Debt Securities, Available-for-sale [Line Items]    
Fair Value 851 978
Unrealized gains 235 320
Unrealized losses $ (79) $ (32)