Fair Value (Details Textuals) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Option, Quantitative Disclosures [Line Items]
Equity securities realized loss	$ 3,000,000
Equity securities realized gain (loss)	0	$ 8,000,000
DTE Electric
Fair Value, Option, Quantitative Disclosures [Line Items]
Equity securities realized gain (loss)	0	8,000,000
Accumulated net unrealized investment gain (loss)
Fair Value, Option, Quantitative Disclosures [Line Items]
Unrealized losses on available for sale securities	0	0
Accumulated net unrealized investment gain (loss) | DTE Electric
Fair Value, Option, Quantitative Disclosures [Line Items]
Unrealized losses on available for sale securities	$ 0	$ 0