Summary of Notional Amounts of Outstanding Foreign Exchange Forwards, Cash Flow Hedging (Detail) € in Millions, ¥ in Millions, £ in Millions, $ in Millions, $ in Millions, $ in Millions	Mar. 31, 2018 CAD ($)	Mar. 31, 2018 EUR (€)	Mar. 31, 2018 GBP (£)	Mar. 31, 2018 JPY (¥)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 CAD ($)	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 GBP (£)	Dec. 31, 2017 JPY (¥)	Dec. 31, 2017 SGD ($)	Dec. 31, 2017 USD ($)
Contracts to Sell US Dollars for GBP [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount					$ 708.7						$ 484.7
Contracts to Sell US Dollars for GBP [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | £			£ 512.9					£ 362.3
Contracts to Sell USD for JPY [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount					24.9						24.3
Contracts to Sell USD for JPY [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | ¥				¥ 2,700.0					¥ 2,700.0
Contracts to Sell USD for CAD [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount					51.7						51.7
Contracts to Sell USD for CAD [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount	$ 64.0					$ 64.0
Contracts to Sell US Dollars for Singapore dollars [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount											39.2
Contracts to Sell US Dollars for Singapore dollars [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount										$ 53.0
Contracts to Sell USD for Euros [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount					$ 74.8						$ 465.2
Contracts to Sell USD for Euros [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | €		€ 60.0					€ 390.0