Accumulated other comprehensive income or loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Changes in AOCI, net of tax
Beginning balance	$ 5,630.2	$ 6,285.9	$ 5,565.0	$ 5,956.7
Income tax effect	(12.2)	(1.2)	(11.4)	24.1
Ending balance	5,835.9	5,570.2	5,835.9	5,570.2
AOCI
Changes in AOCI, net of tax
Beginning balance	(55.2)	(10.4)	(16.9)	(184.0)
Unrealized gain (loss)	(7.4)	(10.0)	(42.6)	126.6
Reclassification of (gain) loss into earnings	(1.7)	(2.0)	(5.6)	9.7
Income tax effect	(12.2)	(1.2)	(11.4)	24.1
Ending balance	(76.5)	(23.6)	(76.5)	(23.6)
Foreign currency translation
Changes in AOCI, net of tax
Beginning balance	(67.8)	(23.8)	(31.0)	(177.4)
Unrealized gain (loss)	(8.3)	(11.5)	(45.3)	116.4
Reclassification of (gain) loss into earnings	0.0	0.0	(0.2)	0.0
Income tax effect	(12.4)	(1.2)	(12.0)	24.5
Ending balance	(88.5)	(36.5)	(88.5)	(36.5)
Derivative instruments
Changes in AOCI, net of tax
Beginning balance	0.0	0.1	0.0	0.2
Unrealized gain (loss)	1.7	1.9	5.4	7.4
Reclassification of (gain) loss into earnings	(1.7)	(2.0)	(5.4)	(7.6)
Income tax effect	0.0	0.0	0.0	0.0
Ending balance	0.0	0.0	0.0	0.0
Defined benefit plans
Changes in AOCI, net of tax
Beginning balance	12.6	13.3	14.1	(6.8)
Unrealized gain (loss)	(0.8)	(0.4)	(2.7)	2.8
Reclassification of (gain) loss into earnings	0.0	0.0	0.0	17.3
Income tax effect	0.2	0.0	0.6	(0.4)
Ending balance	$ 12.0	$ 12.9	$ 12.0	$ 12.9