Accumulated other comprehensive income or loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Changes in AOCI, net of tax
Beginning balance	$ 21.7	$ (85.9)
Unrealized gain (loss)	(33.8)	(66.8)
Reclassification of (gain) loss into earnings	0.7	(0.2)
Income tax effect	(4.7)	(0.4)
Ending balance	(16.1)	(153.3)
Foreign currency translation
Changes in AOCI, net of tax
Beginning balance	51.8	(62.3)
Unrealized gain (loss)	(33.5)	(68.8)
Reclassification of (gain) loss into earnings	0.0	0.0
Income tax effect	(4.7)	0.0
Ending balance	13.6	(131.1)
Derivative instruments
Changes in AOCI, net of tax
Beginning balance	(1.0)	(0.5)
Unrealized gain (loss)	(0.9)	1.6
Reclassification of (gain) loss into earnings	0.7	(0.1)
Income tax effect	0.0	(0.4)
Ending balance	(1.2)	0.6
Defined benefit plans
Changes in AOCI, net of tax
Beginning balance	(29.1)	(23.1)
Unrealized gain (loss)	0.6	0.4
Reclassification of (gain) loss into earnings	0.0	(0.1)
Income tax effect	0.0	0.0
Ending balance	$ (28.5)	$ (22.8)