Related party transactions - Summary of management and performance fees (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Aug. 06, 2020
Related Party Transaction [Line Items]
Total management and performance fees to related parties	$ 93.6	$ 79.8	$ 19.6
Management fees
Related Party Transaction [Line Items]
Total management and performance fees to related parties	17.9	14.5	17.2
Management fees | Third Point LLC, 2020 LPA | Affiliated entity
Related Party Transaction [Line Items]
Fee percentage				1.25%
Performance fees - fixed income and other investments
Related Party Transaction [Line Items]
Total management and performance fees to related parties	0.0	14.0	0.0
Performance fees - fixed income and other investments | Third Point LLC, 2020 LPA | Affiliated entity
Related Party Transaction [Line Items]
Fee percentage				20.00%
Performance fees (before loss carryforward)
Related Party Transaction [Line Items]
Total management and performance fees to related parties	75.7	51.8	49.9
Performance fees - loss carryforward utilized
Related Party Transaction [Line Items]
Total management and performance fees to related parties	$ 0.0	$ (0.5)	$ (47.5)