Acquisitions Acquistions (Details) - USD ($)		3 Months Ended				9 Months Ended	12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 16, 2016	Nov. 01, 2018	Mar. 31, 2018
Business Acquisition [Line Items]
Liquidation Basis of Accounting, Remeasurement, Gain (Loss) on Asset								$ 0	$ 0
Distributed Energy [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred										$ 43,000,000
Payments to Acquire Businesses, Net of Cash Acquired							$ 23,000,000
Business Combination, Ownership Percentage in Acquiree		100.00%					100.00%
Business Combination, Equity Interest in Acquiree, Remeasurement Gain (Loss)		$ 5,000,000					$ 5,000,000
Alto Sertao II [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred				$ 179,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities				346,000,000
Business Combination, Contingent Consideration, Liability												$ 18,000,000
Payments to Acquire Businesses, Net of Cash Acquired				$ 143,000,000
Payment for Contingent Consideration Liability, Financing Activities			$ 12,000,000
Bauru Solar Complex [Member]
Business Acquisition [Line Items]
Asset Acquisition, Purchase Price						$ 152,000,000
Project Financing Disbursed						119,000,000
Asset Acquisition, Consideration Transferred						$ 33,000,000
Na Pua Makani Power Partners [Member]
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired											100.00%
Business Combination, Consideration Transferred		11,000,000			$ 53,000,000
Business Combination, Contingent Consideration		$ 5,000,000			$ 48,000,000
Liquidation Basis of Accounting, Remeasurement, Gain (Loss) on Asset	[1]						$ 32,000,000

[1] Related to the amendment of the Oahu purchase agreement. See Note 24 —Acquisitions for further information.