Income taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Other comprehensive income (loss)	$ (39.6)	$ 49.4	$ 49.5	$ (42.8)	$ 9.8	$ 6.7
Decrease in valuation allowance, deferred tax asset					$ 55.0
Valuation Allowance of Deferred Tax Assets
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Other comprehensive income (loss)	$ 10.9