Income taxes - Components of Comprehensive Provision for Income Taxes Allocation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Income taxes
Expected tax expense at U.S. federal statutory income tax rate of 21%	$ 3.2	$ 7.9	$ 9.7	$ 11.7
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%	21.00%
Non-U.S. tax rates	$ (0.3)	$ (0.1)	$ 0.2	$ (0.1)
Incremental net tax benefit on earnings and losses of U.S. and non-U.S. tax group companies	(2.1)	(3.5)	(2.5)	(4.3)
Global intangible low-taxed income, net	1.9	1.1	2.5	1.4
Valuation allowance, net	5.3	1.7	5.5	2.5
Nondeductible expenses	0.8	0.4	1.3	0.6
U.S. state income taxes and other, net	(0.8)	0.4	(0.7)	0.5
Income tax expense	8.0	7.9	16.0	12.3
Comprehensive provision for income taxes allocable to:
Net income	8.0	7.9	16.0	12.3
Other comprehensive income (loss):
Currency translation	1.7	0.2	3.6	(2.1)
Pension plans	0.2	0.3	0.4	0.6
Other		(0.1)		(0.2)
Total	$ 9.9	$ 8.3	$ 20.0	$ 10.6