Related party transactions - Summary of management and performance fees (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Aug. 06, 2020
Related Party Transaction [Line Items]
Total management and performance fees to related parties	$ 55.6	$ 20.4	$ 113.8	$ 27.5
Management fees
Related Party Transaction [Line Items]
Total management and performance fees to related parties	5.3	3.5	14.1	10.6
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	12.5	0.0	12.5
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	50.3	25.3	99.7	4.9
Performance fees - loss carryforward utilized
Related Party Transaction [Line Items]
Total management and performance fees to related parties	$ 0.0	$ (20.9)	$ 0.0	$ (0.5)