Allowance for expected credit losses - Summary of allowance for expected credit losses (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Receivables [Abstract]
Insurance and reinsurance balances receivable, net	$ 1,708.2	$ 441.9
Loss and loss adjustment expenses recoverable, net	1,215.3	14.4	$ 5.5	$ 2.0
Other assets	14.5	0.0
Total assets in scope	$ 2,938.0	$ 456.3