Location and Fair Values of Derivative Financial Instruments (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Derivative
Asset Derivatives Fair Value	$ 23.4	$ 19.8
Designated as Hedging Instrument | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	23.0	19.7
Designated as Hedging Instrument | Other Long-term Investments | Foreign Exchange Contracts | Cash Flow Hedging
Derivative
Asset Derivatives Fair Value	15.1	16.4
Designated as Hedging Instrument | Other Long-term Investments | Foreign Exchange Contracts | Fair Value Hedging
Derivative
Asset Derivatives Fair Value	7.9	3.3
Designated as Hedging Instrument | Other Liabilities
Derivative
Liability Derivatives Fair Value	21.4	35.4
Designated as Hedging Instrument | Other Liabilities | Foreign Exchange Contracts | Cash Flow Hedging
Derivative
Liability Derivatives Fair Value	9.4	9.4
Designated as Hedging Instrument | Other Liabilities | Foreign Exchange Contracts | Fair Value Hedging
Derivative
Liability Derivatives Fair Value	12.0	26.0
Not Designated as Hedging Instrument | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	0.4	0.1
Not Designated as Hedging Instrument | Other Long-term Investments | Foreign Exchange Contracts
Derivative
Asset Derivatives Fair Value	0.0	0.0
Not Designated as Hedging Instrument | Other Long-term Investments | Credit Default Swaps
Derivative
Asset Derivatives Fair Value	0.0	0.1
Not Designated as Hedging Instrument | Other Long-term Investments | Forwards
Derivative
Asset Derivatives Fair Value	0.4	0.0
Not Designated as Hedging Instrument | Other Long-term Investments | Embedded Derivative in Modified Coinsurance Arrangement
Derivative
Asset Derivatives Fair Value	0.0	0.0
Not Designated as Hedging Instrument | Other Liabilities
Derivative
Liability Derivatives Fair Value	44.2	64.1
Not Designated as Hedging Instrument | Other Liabilities | Foreign Exchange Contracts
Derivative
Liability Derivatives Fair Value	22.8	23.8
Not Designated as Hedging Instrument | Other Liabilities | Credit Default Swaps
Derivative
Liability Derivatives Fair Value	0.1	0.0
Not Designated as Hedging Instrument | Other Liabilities | Forwards
Derivative
Liability Derivatives Fair Value	0.1	0.5
Not Designated as Hedging Instrument | Other Liabilities | Embedded Derivative in Modified Coinsurance Arrangement
Derivative
Liability Derivatives Fair Value	$ 21.2	$ 39.8