Stockholders' equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Accumulated other comprehensive income (loss) (net of tax and noncontrolling interest):
Balance at beginning of period			$ 1,036.1
Balance at end of period	$ 1,071.5		1,071.5
Marketable Securities
Accumulated other comprehensive income (loss) (net of tax and noncontrolling interest):
Balance at beginning of period	1.7	$ 1.7	1.7	$ 1.7
Currency Translation
Accumulated other comprehensive income (loss) (net of tax and noncontrolling interest):
Balance at beginning of period	(100.3)	(102.4)	(111.7)	(88.8)
Other comprehensive income (loss)	9.5	1.2	20.9	(12.4)
Balance at end of period	(90.8)	(101.2)	(90.8)	(101.2)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss) (net of tax and noncontrolling interest):
Balance at beginning of period	(48.9)	(58.3)	(49.4)	(58.8)
Other comprehensive income (loss)	0.4	0.5	0.9	1.0
Balance at end of period	(48.5)	(57.8)	(48.5)	(57.8)
Accumulated Defined Benefit Plans Adjustment | OPEB
Accumulated other comprehensive income (loss) (net of tax and noncontrolling interest):
Balance at beginning of period	0.1	0.4	0.2	0.4
Other comprehensive income (loss)		(0.1)	(0.1)	(0.1)
Balance at end of period	0.1	0.3	0.1	0.3
Total Accumulated Other Comprehensive Loss
Accumulated other comprehensive income (loss) (net of tax and noncontrolling interest):
Balance at beginning of period	(147.4)	(158.6)	(159.2)	(145.5)
Other comprehensive income (loss)	9.9	1.6	21.7	(11.5)
Balance at end of period	$ (137.5)	$ (157.0)	$ (137.5)	$ (157.0)