Debt - Details of Senior Notes (Detail) - Unsecured Debt [Member]	Dec. 31, 2016 USD ($)
5.50% Senior Notes [Member]
Debt Instrument [Line Items]
Principal amount	$ 750,000,000
Stated interest rate percentage	5.50%
6.125% Senior Notes [Member]
Debt Instrument [Line Items]
Principal amount	$ 500,000,000
Stated interest rate percentage	6.125%
4.625% Senior Notes [Member]
Debt Instrument [Line Items]
Principal amount	$ 500,000,000
Stated interest rate percentage	4.625%