Acquisitions and Exit Activities (Acquisitions) (Details) - DTE Electric $ in Millions			12 Months Ended
	Oct. 01, 2015 USD ($) MW	Jan. 21, 2015 USD ($) MW	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Business Acquisition [Line Items]
Total purchase price			$ 310	$ 0	$ 0
Natural Gas Facility in Carson City Michigan
Business Acquisition [Line Items]
Gas facility capacity | MW		732
Total purchase price		$ 241
Natural Gas Facility in East China Township Michigan
Business Acquisition [Line Items]
Gas facility capacity | MW	350
Cash consideration and total purchase price	$ 69