Variable Interest Entities (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($) MW
Variable Interest Entity, Not Primary Beneficiary | Copper Mountain Solar 3 | Nevada
Variable Interest Entity [Line Items]
Generating Capacity (MW AC) | MW	128
Power Purchase Agreement Term (in Years)	20 years
Maximum Exposure to Loss	$ 175
Variable Interest Entity, Not Primary Beneficiary | Mesquite Solar 1 | Arizona
Variable Interest Entity [Line Items]
Generating Capacity (MW AC) | MW	83
Power Purchase Agreement Term (in Years)	20 years
Maximum Exposure to Loss	$ 102
Variable Interest Entity, Not Primary Beneficiary | Copper Mountain Solar 2 | Nevada
Variable Interest Entity [Line Items]
Generating Capacity (MW AC) | MW	75
Power Purchase Agreement Term (in Years)	25 years
Maximum Exposure to Loss	$ 83
Variable Interest Entity, Not Primary Beneficiary | California Solar | California
Variable Interest Entity [Line Items]
Generating Capacity (MW AC) | MW	55
Power Purchase Agreement Term (in Years)	25 years
Maximum Exposure to Loss	$ 64
Variable Interest Entity, Not Primary Beneficiary | Broken Bow II | Nebraska
Variable Interest Entity [Line Items]
Generating Capacity (MW AC) | MW	38
Power Purchase Agreement Term (in Years)	25 years
Maximum Exposure to Loss	$ 44
Variable Interest Entity, Primary Beneficiary | Texas Solar 4
Variable Interest Entity [Line Items]
Percentage of variable interests	80.00%
Maximum exposure for consolidated investments	$ 7
Variable Interest Entity, Primary Beneficiary | Texas Solar 4 | Texas
Variable Interest Entity [Line Items]
Generating Capacity (MW AC) | MW	32
Power Purchase Agreement Term (in Years)	25 years
Maximum Exposure to Loss	$ 47
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure
Variable Interest Entity [Line Items]
Percentage of variable interests	50.00%