Location and Fair Values of Derivative Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Derivative
Asset Derivatives Fair Value	$ 19.8	$ 27.5
Designated as Hedging Instrument | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	19.7	27.0
Designated as Hedging Instrument | Other Long-term Investments | Fair Value Hedging
Derivative
Asset Derivatives Fair Value		7.6
Designated as Hedging Instrument | Other Long-term Investments | Foreign Exchange Contracts | Cash Flow Hedging
Derivative
Asset Derivatives Fair Value	16.4	19.4
Designated as Hedging Instrument | Other Long-term Investments | Foreign Exchange Contracts | Fair Value Hedging
Derivative
Asset Derivatives Fair Value	3.3	7.6
Designated as Hedging Instrument | Other Long-term Investments | Interest Rate Swaps | Fair Value Hedging
Derivative
Asset Derivatives Fair Value		0.0
Designated as Hedging Instrument | Other Liabilities
Derivative
Liability Derivatives Fair Value	35.4	12.2
Designated as Hedging Instrument | Other Liabilities | Fair Value Hedging
Derivative
Liability Derivatives Fair Value		5.6
Designated as Hedging Instrument | Other Liabilities | Foreign Exchange Contracts | Cash Flow Hedging
Derivative
Liability Derivatives Fair Value	9.4	6.6
Designated as Hedging Instrument | Other Liabilities | Foreign Exchange Contracts | Fair Value Hedging
Derivative
Liability Derivatives Fair Value	26.0	5.0
Designated as Hedging Instrument | Other Liabilities | Interest Rate Swaps | Fair Value Hedging
Derivative
Liability Derivatives Fair Value		0.6
Not Designated as Hedging Instrument | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	0.1	0.5
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	0.5
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 Long-term Investments | Forwards
Derivative
Asset Derivatives Fair Value	0.0
Not Designated as Hedging Instrument | Other Liabilities
Derivative
Liability Derivatives Fair Value	64.1	45.2
Not Designated as Hedging Instrument | Other Liabilities | Foreign Exchange Contracts
Derivative
Liability Derivatives Fair Value	23.8	22.4
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	39.8	$ 22.8
Not Designated as Hedging Instrument | Other Liabilities | Forwards
Derivative
Liability Derivatives Fair Value	$ 0.5