Location and Fair Values of Derivative Financial Instruments (Detail) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Derivative
Derivative, Notional Amount	$ 1,672.9	$ 970.5
Asset Derivatives Fair Value	128.1	39.5
Other Long-term Investments
Derivative
Asset Derivatives Fair Value	128.1	39.5
Other Liabilities
Derivative
Liability Derivatives Fair Value	75.8	65.1
Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	1,400.2	679.8
Designated as Hedging Instrument \| Cash Flow Hedging
Derivative
Derivative, Notional Amount	842.0
Designated as Hedging Instrument \| Forwards \| Cash Flow Hedging
Derivative
Derivative, Notional Amount	664.0
Designated as Hedging Instrument \| Interest Rate Swaps \| Cash Flow Hedging
Derivative
Derivative, Notional Amount	178.0	181.3
Designated as Hedging Instrument \| Interest Rate Swaps \| Fair Value Hedging
Derivative
Derivative, Notional Amount	558.2	498.5
Designated as Hedging Instrument \| Other Long-term Investments
Derivative
Asset Derivatives Fair Value	120.8	38.1
Designated as Hedging Instrument \| Other Long-term Investments \| Cash Flow Hedging
Derivative
Asset Derivatives Fair Value	22.4
Designated as Hedging Instrument \| Other Long-term Investments \| Forwards \| Cash Flow Hedging
Derivative
Asset Derivatives Fair Value	0.0
Designated as Hedging Instrument \| Other Long-term Investments \| Interest Rate Swaps \| Cash Flow Hedging
Derivative
Asset Derivatives Fair Value	22.4	16.2
Designated as Hedging Instrument \| Other Long-term Investments \| Interest Rate Swaps \| Fair Value Hedging
Derivative
Asset Derivatives Fair Value	98.4	21.9
Designated as Hedging Instrument \| Other Liabilities
Derivative
Liability Derivatives Fair Value	37.0	12.7
Designated as Hedging Instrument \| Other Liabilities \| Cash Flow Hedging
Derivative
Liability Derivatives Fair Value	31.2
Designated as Hedging Instrument \| Other Liabilities \| Forwards \| Cash Flow Hedging
Derivative
Liability Derivatives Fair Value	29.0
Designated as Hedging Instrument \| Other Liabilities \| Interest Rate Swaps \| Cash Flow Hedging
Derivative
Liability Derivatives Fair Value	2.2	7.0
Designated as Hedging Instrument \| Other Liabilities \| Interest Rate Swaps \| Fair Value Hedging
Derivative
Liability Derivatives Fair Value	5.8	5.7
Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	272.7	290.7
Not Designated as Hedging Instrument \| Credit Default Swaps
Derivative
Derivative, Notional Amount		11.6
Not Designated as Hedging Instrument \| Forwards
Derivative
Derivative, Notional Amount	54.3	41.7
Not Designated as Hedging Instrument \| Interest Rate Swaps
Derivative
Derivative, Notional Amount	148.2	148.2
Not Designated as Hedging Instrument \| Total Return Swap
Derivative
Derivative, Notional Amount	70.2	89.2
Not Designated as Hedging Instrument \| Embedded Derivative in Modified Coinsurance Arrangement
Derivative
Derivative, Notional Amount	0.0	0.0
Not Designated as Hedging Instrument \| Other Long-term Investments
Derivative
Asset Derivatives Fair Value	7.3	1.4
Not Designated as Hedging Instrument \| Other Long-term Investments \| Credit Default Swaps
Derivative
Asset Derivatives Fair Value		0.0
Not Designated as Hedging Instrument \| Other Long-term Investments \| Forwards
Derivative
Asset Derivatives Fair Value	7.3	0.0
Not Designated as Hedging Instrument \| Other Long-term Investments \| Interest Rate Swaps
Derivative
Asset Derivatives Fair Value	0.0	1.4
Not Designated as Hedging Instrument \| Other Long-term Investments \| Total Return Swap
Derivative
Asset Derivatives Fair Value	0.0	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	38.8	52.4
Not Designated as Hedging Instrument \| Other Liabilities \| Credit Default Swaps
Derivative
Liability Derivatives Fair Value		0.0
Not Designated as Hedging Instrument \| Other Liabilities \| Forwards
Derivative
Liability Derivatives Fair Value	0.0	0.0
Not Designated as Hedging Instrument \| Other Liabilities \| Interest Rate Swaps
Derivative
Liability Derivatives Fair Value	19.4	22.3
Not Designated as Hedging Instrument \| Other Liabilities \| Total Return Swap
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	$ 19.4	$ 30.1

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Nominal or face amount used to calculate payment on derivative.

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