Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis and Subject to Fair Value Disclosure Requirements (Detail) - USD ($) $ in Millions	1 Months Ended
	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Money market funds		$ 246	$ 501
Quoted Price as in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Money market funds		246	501
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Money market funds		0	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Money market funds		0	0
Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate swap, agreement period	5 years
Notional amount of contracts	$ 500	500	$ 0
Interest rate swap		7
Interest Rate Swap | Quoted Price as in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate swap		0
Interest Rate Swap | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate swap		7
Interest Rate Swap | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest rate swap		$ 0