Leases and commitments - Components of Lease Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Operating lease cost	$ 36.7	$ 39.7	$ 42.3
Finance lease cost
Amortization of right-of-use assets	1.2	1.8	1.7
Interest on lease liabilities	0.0	0.1	0.2
Total finance lease cost	1.2	1.9	1.9
Short-term lease costs	0.7	0.9	1.4
Variable lease cost	11.6	11.5	10.3
Sublease income	(1.8)	(4.4)	(12.1)
Total lease cost	$ 48.4	$ 49.6	$ 43.8