Summary of Significant Accounting Policies - Summary of Financial Information for Joint Ventures (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Method Investments and Joint Ventures [Abstract]
Total assets	$ 1,924	$ 1,703
Total liabilities	1,451	1,347
Revenues	731	731	$ 693
Net income	$ 114	$ 261	$ 80