Cost-reduction actions - Liabilities and Expected Future Payments Related to Work-Force Reduction Actions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2022
Restructuring Reserve [Roll Forward]
Additional provisions	$ 23.2	$ 95.5	$ 28.7
Work-Force Reductions
Restructuring Reserve [Roll Forward]
Balance at beginning of period	55.9	49.8	86.2
Additional provisions	12.3	39.0	25.7
Payments	(38.5)	(21.5)	(57.7)
Changes in estimates	(11.9)	(13.5)	(3.6)
Translation adjustments	(1.5)	2.1	(0.8)
Balance at end of period	16.3	55.9	49.8
Expected future payments on balance at December 31, 2021:
In 2022	14.9
Beyond 2022	14.9
Work-Force Reductions | Forecast
Expected future payments on balance at December 31, 2021:
In 2022				$ 1.4
Beyond 2022				1.4
Work-Force Reductions | U.S.
Restructuring Reserve [Roll Forward]
Balance at beginning of period	13.1	5.2	6.1
Additional provisions	7.9	13.8	4.6
Payments	(13.2)	(3.2)	(4.0)
Changes in estimates	(2.1)	(2.7)	(1.5)
Translation adjustments	0.0	0.0	0.0
Balance at end of period	5.7	13.1	5.2
Expected future payments on balance at December 31, 2021:
In 2022	5.7
Beyond 2022	5.7
Work-Force Reductions | U.S. | Forecast
Expected future payments on balance at December 31, 2021:
In 2022				0.0
Beyond 2022				0.0
Work-Force Reductions | International
Restructuring Reserve [Roll Forward]
Balance at beginning of period	42.8	44.6	80.1
Additional provisions	4.4	25.2	21.1
Payments	(25.3)	(18.3)	(53.7)
Changes in estimates	(9.8)	(10.8)	(2.1)
Translation adjustments	(1.5)	2.1	(0.8)
Balance at end of period	10.6	$ 42.8	$ 44.6
Expected future payments on balance at December 31, 2021:
In 2022	9.2
Beyond 2022	$ 9.2
Work-Force Reductions | International | Forecast
Expected future payments on balance at December 31, 2021:
In 2022				1.4
Beyond 2022				$ 1.4