Location and Fair Values of Derivative Financial Instruments (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Derivative
Asset Derivatives Fair Value	$ 27.0	$ 32.7
Designated as Hedging Instrument | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	27.0	32.7
Designated as Hedging Instrument | Other Liabilities
Derivative
Liability Derivatives Fair Value	20.7	20.3
Designated as Hedging Instrument | Interest Rate Swaps | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	0.0	0.0
Designated as Hedging Instrument | Interest Rate Swaps | Other Liabilities
Derivative
Liability Derivatives Fair Value	4.3	6.9
Designated as Hedging Instrument | Foreign Exchange Contracts | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	27.0	32.7
Designated as Hedging Instrument | Foreign Exchange Contracts | Other Liabilities
Derivative
Liability Derivatives Fair Value	16.4	13.4
Not Designated as Hedging Instrument | Other Liabilities
Derivative
Liability Derivatives Fair Value	63.8	79.2
Not Designated as Hedging Instrument | Interest Rate Swaps | Other Liabilities
Derivative
Liability Derivatives Fair Value		0.7
Not Designated as Hedging Instrument | Foreign Exchange Contracts | Other Liabilities
Derivative
Liability Derivatives Fair Value	31.4	31.4
Not Designated as Hedging Instrument | Credit Risk Contract | Other Liabilities
Derivative
Liability Derivatives Fair Value	0.5	0.4
Not Designated as Hedging Instrument | Embedded Derivative in Modified Coinsurance Arrangement | Other Liabilities
Derivative
Liability Derivatives Fair Value	$ 31.9	$ 46.7