Variable Interest Entities - Summary of VIEs (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) MW
Variable Interest Entity, Not Primary Beneficiary | Copper Mountain Solar 3
Variable Interest Entity [Line Items]
Generating Capacity Owned (MW AC) | MW	128
Power Purchase Agreement Term in Years	20 years
Maximum Exposure to Loss	$ 175,000,000
Variable Interest Entity, Not Primary Beneficiary | Mesquite Solar 1
Variable Interest Entity [Line Items]
Generating Capacity Owned (MW AC) | MW	83
Power Purchase Agreement Term in Years	20 years
Maximum Exposure to Loss	$ 103,000,000
Variable Interest Entity, Not Primary Beneficiary | Copper Mountain Solar 2
Variable Interest Entity [Line Items]
Generating Capacity Owned (MW AC) | MW	75
Power Purchase Agreement Term in Years	25 years
Maximum Exposure to Loss	$ 82,000,000
Variable Interest Entity, Not Primary Beneficiary | California Solar
Variable Interest Entity [Line Items]
Generating Capacity Owned (MW AC) | MW	55
Power Purchase Agreement Term in Years	25 years
Maximum Exposure to Loss	$ 63,000,000
Variable Interest Entity, Not Primary Beneficiary | Broken Bow II
Variable Interest Entity [Line Items]
Generating Capacity Owned (MW AC) | MW	38
Power Purchase Agreement Term in Years	25 years
Maximum Exposure to Loss	$ 44,000,000
Variable Interest Entity, Primary Beneficiary | Texas Solar 4
Variable Interest Entity [Line Items]
Generating Capacity Owned (MW AC) | MW	32
Power Purchase Agreement Term in Years	25 years
Maximum Exposure to Loss	$ 19,000,000
Percentage of variable interests	80.00%
Maximum exposure for consolidated investments	$ 7,000,000
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure
Variable Interest Entity [Line Items]
Percentage of variable interests	50.00%