Location and Fair Values of Derivative Financial Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivative
Asset Derivatives Fair Value	$ 17.6	$ 19.8
Designated as Hedging Instrument | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	17.4	19.7
Designated as Hedging Instrument | Other Long-term Investments | Foreign Exchange Contracts | Cash Flow Hedging
Derivative
Asset Derivatives Fair Value	15.4	16.4
Designated as Hedging Instrument | Other Long-term Investments | Foreign Exchange Contracts | Fair Value Hedging
Derivative
Asset Derivatives Fair Value	2.0	3.3
Designated as Hedging Instrument | Other Liabilities
Derivative
Liability Derivatives Fair Value	32.3	35.4
Designated as Hedging Instrument | Other Liabilities | Foreign Exchange Contracts | Cash Flow Hedging
Derivative
Liability Derivatives Fair Value	10.1	9.4
Designated as Hedging Instrument | Other Liabilities | Foreign Exchange Contracts | Fair Value Hedging
Derivative
Liability Derivatives Fair Value	22.2	26.0
Not Designated as Hedging Instrument | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	0.2	0.1
Not Designated as Hedging Instrument | Other Long-term Investments | Forwards
Derivative
Asset Derivatives Fair Value	0.1	0.0
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	0.1	0.1
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	45.5	64.1
Not Designated as Hedging Instrument | Other Liabilities | Forwards
Derivative
Asset Derivatives Fair Value		0.5
Liability Derivatives Fair Value	0.1
Not Designated as Hedging Instrument | Other Liabilities | Foreign Exchange Contracts
Derivative
Liability Derivatives Fair Value	22.5	23.8
Not Designated as Hedging Instrument | Other Liabilities | Credit Default Swaps
Derivative
Liability Derivatives Fair Value	0.0	0.0
Not Designated as Hedging Instrument | Other Liabilities | Embedded Derivative in Modified Coinsurance Arrangement
Derivative
Liability Derivatives Fair Value	$ 22.9	$ 39.8