Reinsurance Retention Policy, Retrocession Premium, Interest Rate

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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Nominal or face amount used to calculate payment on derivative.

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Amount of gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3).

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Amount of gain (loss) from the increase (decrease) in fair value of foreign currency derivatives and nonderivative instruments designated as fair value hedging instruments which were recognized in earnings, net of offsets by the gain (loss) on the hedged item to the extent that the fair value hedge was determined to be effective.

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Derivative Contracts - Additional Information (Details) - USD ($) $ in Millions		12 Months Ended
	Oct. 01, 2022	Dec. 31, 2023	Dec. 31, 2022
Reinsurance Contracts [Axis]: Funds withheld credited with interest for periods after October 1, 2022
Derivative Instruments, Gain (Loss) [Line Items]
Reinsurance Retention Policy, Retrocession Premium, Interest Rate	1.75%
Level 3 \| Liability \| Fair Value, Recurring [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Liability, increase (decrease) in fv included in net income		$ 15.2	$ (14.5)
Foreign exchange contracts \| Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Purchase of US and foreign exchange		1,802.9	1,675.3
Gain (loss) to net income from derivative instruments		10.9	(66.0)
Foreign exchange contracts \| Not Designated as Hedging Instrument \| Derivative liabilities
Derivative Instruments, Gain (Loss) [Line Items]
Purchase of US and foreign exchange		540.8	729.5
Foreign exchange contracts \| Net change from current period hedged transactions \| Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on foreign currency fair value hedge derivatives		(14.0)	15.4
Foreign exchange contracts \| General, administrative and corporate expenses \| Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on foreign currency fair value hedge derivatives		(8.1)	5.9
Foreign exchange contracts \| General, administrative and corporate expenses \| Designated as Hedging Instrument \| Forecast
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on foreign currency fair value hedge derivatives		0.3
Loss Portfolio Transfer \| Level 3 \| Liability \| Fair Value, Recurring [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Liability, increase (decrease) in fv included in net income		$ 15.2	$ (14.5)