Financial Instruments and Fair Value Measurements - Foreign Currency Contracts Activity (Detail) - Forwards [Member]	6 Months Ended
	Jun. 30, 2018 USD ($) Derivative	Jun. 30, 2017 USD ($) Derivative
CAD
Derivative [Line Items]
Notional amounts at January 1	$ 99,000,000	$ 100,000,000
New contracts	100,000,000	99,000,000
Matured, expired or settled contracts	(99,000,000)	(100,000,000)
Notional amounts at June 30	$ 100,000,000	$ 99,000,000
Weighted average forward rate at June 30	1.28	1.34
Active contracts at June 30 | Derivative	2	2
EUR
Derivative [Line Items]
Notional amounts at January 1	$ 0
New contracts	35,000,000
Matured, expired or settled contracts	0
Notional amounts at June 30	$ 35,000,000
Weighted average forward rate at June 30	1.16
Active contracts at June 30 | Derivative	1
GBP
Derivative [Line Items]
Notional amounts at January 1		$ 46,000,000
New contracts		127,000,000
Matured, expired or settled contracts		(173,000,000)
Notional amounts at June 30		$ 0
Weighted average forward rate at June 30		0
Active contracts at June 30 | Derivative		0