Derivatives - Classification and net impact on earnings of derivatives (Details) - Derivatives not designated as hedging instruments $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)
Foreign currency swaps | Foreign exchange (gains) losses
Derivative Instruments, Gain (Loss) [Line Items]
Net impact on earnings	$ 0.2
Foreign currency forwards | Foreign exchange (gains) losses
Derivative Instruments, Gain (Loss) [Line Items]
Net impact on earnings	(1.3)
Foreign currency futures contracts | Foreign exchange (gains) losses
Derivative Instruments, Gain (Loss) [Line Items]
Net impact on earnings	(8.0)
Foreign currency call options | Foreign exchange (gains) losses
Derivative Instruments, Gain (Loss) [Line Items]
Net impact on earnings	0.4
Weather derivatives | Net corporate and other expenses
Derivative Instruments, Gain (Loss) [Line Items]
Net impact on earnings	0.9
Equity warrants | Net realized and unrealized investment gains (losses)
Derivative Instruments, Gain (Loss) [Line Items]
Net impact on earnings	$ (0.3)