Significant Accounting Policies Significant Accounting Policies (Other Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Other Nonoperating Income, by Component [Line Items]
Equity earnings of equity method investees	$ 32	$ 25	$ 53	$ 51
Income from REF entities	25	22	48	40
Contract services	12	4	32	8
Allowance for equity funds used during construction	6	5	13	12
Gains from equity securities	1	5	1	13
Other	6	5	16	6
Total other income	82	66	163	130
DTE Electric
Schedule of Other Nonoperating Income, by Component [Line Items]
Contract services	13	5	33	9
Allowance for equity funds used during construction	4	4	9	10
Gains from equity securities	1	5	1	13
Other	4	3	6	4
Total other income	$ 22	$ 17	$ 49	$ 36