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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, 2016
Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]    
Equity securities, fair value $ 872 $ 731
Debt securities, fair value 439 499
Cash and cash equivalents 10 6
Fair Value 1,321 1,236
Equity securities, unrealized gains 213 195
Debt securities, unrealized gains 25 16
Unrealized Gains 238 211
Equity securities, unrealized losses (47) (68)
Debt securities, unrealized losses (1) (4)
Unrealized Losses $ (48) $ (72)