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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, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Equity securities, fair value $ 978 $ 887
Fixed income securities, fair value 495 425
Private equity securities 5 0
Cash equivalents, fair value 14 8
Fair Value 1,492 1,320
Equity securities, unrealized gain 320 222
Fixed income securities, unrealized gain 13 11
Unrealized Gains 333 233
Equity securities, unrealized loss (32) (46)
Fixed income securities, unrealized loss (3) (5)
Unrealized Losses $ (35) $ (51)