Acquisitions and Dispositions (Schedule of Acquisitions of Solar Projects) (Details) $ in Millions		1 Months Ended				2 Months Ended				9 Months Ended
		Aug. 31, 2015 USD ($)	Jul. 31, 2015 USD ($)	Apr. 30, 2015 USD ($) project MW		Aug. 31, 2015 USD ($) project MW	Jul. 31, 2015 USD ($) project MW	May 31, 2015 USD ($)		Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Business Acquisition [Line Items]
Acquisition of solar development projects										$ 21	$ 278
EC&R NA Solar PV, LLC
Business Acquisition [Line Items]
Number of Projects | project				1
Initial Acquisition Cost	[1]			$ 66
Acquisition of solar development projects	[2]							$ 66
MW Capacity | MW				20
EDF Renewable Development, Inc.
Business Acquisition [Line Items]
Number of Projects | project				3	[3]		1
Initial Acquisition Cost	[1]			$ 106	[3]		$ 68
Acquisition of solar development projects	[2]		$ 68					$ 106	[3]
MW Capacity | MW				24	[3]		18
SunPeak Solar, LLC
Business Acquisition [Line Items]
Number of Projects | project						1
Initial Acquisition Cost	[1]					$ 42
Acquisition of solar development projects	[2]	$ 71
MW Capacity | MW						20

[1] The purchase price was primarily allocated to Property, Plant and Equipment.

[2] Includes acquisition cost.

[3] One of the projects, Marin Carport, began commercial operations in 2016.