Variable Interest Entities - Summary of VIEs (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) MW
Variable Interest Entity, Not Primary Beneficiary | Great Valley Solar
Variable Interest Entity [Line Items]
Generating Capacity Owned (MW AC) | MW	200
Maximum Exposure to Loss	$ 281,000,000
Variable Interest Entity, Not Primary Beneficiary | Great Valley Solar | Minimum
Variable Interest Entity [Line Items]
Power Purchase Agreement Term in Years	15 years
Variable Interest Entity, Not Primary Beneficiary | Great Valley Solar | Maximum
Variable Interest Entity [Line Items]
Power Purchase Agreement Term in Years	20 years
Variable Interest Entity, Not Primary Beneficiary | Copper Mountain Solar - Mesquite Solar
Variable Interest Entity [Line Items]
Generating Capacity Owned (MW AC) | MW	344
Maximum Exposure to Loss	$ 485,000,000
Variable Interest Entity, Not Primary Beneficiary | Copper Mountain Solar - Mesquite Solar | Minimum
Variable Interest Entity [Line Items]
Power Purchase Agreement Term in Years	20 years
Variable Interest Entity, Not Primary Beneficiary | Copper Mountain Solar - Mesquite Solar | Maximum
Variable Interest Entity [Line Items]
Power Purchase Agreement Term in Years	25 years
Variable Interest Entity, Primary Beneficiary | Great Valley Solar
Variable Interest Entity [Line Items]
Maximum exposure for consolidated investments	$ 33,000,000
Variable Interest Entity, Primary Beneficiary | Copper Mountain Solar - Mesquite Solar
Variable Interest Entity [Line Items]
Maximum exposure for consolidated investments	$ 71,000,000
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	$ 20,000,000
Maximum exposure for consolidated investments	$ 7,000,000