Significant Accounting Policies Significant Accounting Policies (Other Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule of Other Nonoperating Income, by Component [Line Items]
Equity earnings of equity method investees	$ 46	$ 26	$ 99	$ 77
Income from REF entities	27	20	75	60
Contract services	11	9	43	17
Allowance for equity funds used during construction	7	5	20	17
Gains from equity securities	5	6	6	19
Other	3	8	19	14
Total other income	99	74	262	204
DTE Electric
Schedule of Other Nonoperating Income, by Component [Line Items]
Contract services	11	9	44	18
Allowance for equity funds used during construction	5	4	14	14
Gains from equity securities	5	6	6	19
Other	2	2	8	6
Total other income	$ 23	$ 21	$ 72	$ 57