Significant Accounting Policies Significant Accounting Policies (Other Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of Other Nonoperating Income, by Component [Line Items]
Income from REF entities	$ 23	$ 18
Equity earnings of equity method investees	21	26
Contract services	20	4
Allowance for equity funds used during construction	7	7
Gains from equity securities	0	8
Other	10	1
Total other income	81	64
DTE Electric
Schedule of Other Nonoperating Income, by Component [Line Items]
Contract services	20	4
Allowance for equity funds used during construction	5	6
Gains from equity securities	0	8
Other	2	1
Total other income	$ 27	$ 19