Fair Value Measurements - Carrying Amount and Estimated Fair Values of Financial Assets and Liabilities (Parenthetical) (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred debt issuance costs and original issue discount	$ 25	$ 11
CMBS Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt issuance cost net	$ 25
Term Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred debt issuance costs and original issue discount		$ 11