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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, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Equity securities, fair value $ 949 $ 887
Fixed income securities, fair value 484 425
Cash equivalents, fair value 6 8
Fair Value 1,439 1,320
Equity securities, unrealized gains 287 222
Fixed income securities, unrealized gains 14 11
Unrealized Gains 301 233
Equity securities, unrealized losses (34) (46)
Fixed income securities, unrealized losses (2) (5)
Unrealized Losses $ (36) $ (51)