Significant Accounting Policies Significant Accounting Policies (Other Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Schedule of Other Nonoperating Income, by Component [Line Items]
Income from REF entities	$ 27	$ 23
Equity earnings of equity method investees	23	21
Gains from equity securities	17	0
Contract services	8	20
Allowance for equity funds used during construction	7	7
Other	6	10
Total other income	88	81
DTE Electric
Schedule of Other Nonoperating Income, by Component [Line Items]
Gains from equity securities	17	0
Contract services	8	20
Allowance for equity funds used during construction	6	5
Other	2	2
Total other income	$ 33	$ 27