Tax Equity Financing Arrangements - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended
	Feb. 28, 2017	Mar. 31, 2017	Dec. 31, 2016
Tax Equity Financing Arrangements [Line Items]
Accrued interest average rate		5.30%	5.40%
Assets of variable interest entities (VIEs)		$ 1,293,000,000	$ 1,343,000,000
Liabilities of variable interest entities (VIEs)		218,000,000	244,000,000
Equity method investments of variable interest entities (VIEs)		384,000,000	387,000,000
Upfront cash payments		0
Variable Interest Entity, Primary Beneficiary [Member]
Tax Equity Financing Arrangements [Line Items]
Equity method investments of variable interest entities (VIEs)		$ 159,000,000	$ 161,000,000
Locust Ridge Wind Farm, LLC [Member]
Tax Equity Financing Arrangements [Line Items]
Acquisition of equity investor's interest	$ 5,000,000