Acquisitions Acquistions (Details) - USD ($) $ in Millions			12 Months Ended
	Dec. 31, 2015	Feb. 18, 2015	Sep. 16, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill, Acquired During Period				$ 16
Main street power [Member]
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired		100.00%
Business Combination, Consideration Transferred		$ 25
Payments to Acquire Businesses, Gross		20
Business Combination, Consideration Transferred, Other		$ 5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	$ 4			$ 4
Goodwill, Acquired During Period	$ 16
Distributed energy [Domain]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			$ 43