Accumulated other comprehensive income (loss) - Reclasses Out Of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	$ 570.2	$ 252.6
Other comprehensive income	36.0	49.4
Ending balance	605.0	369.8
Benefit Plan Adjustments
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	(290.7)
Other comprehensive income (loss) before reclassifications	(0.6)
Amounts reclassified from accumulated other comprehensive loss to net income	0.5
Other comprehensive income	(0.1)	7.0
Ending balance	(290.8)
Foreign Currency Translation Adjustments
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	(433.8)
Other comprehensive income (loss) before reclassifications	44.7
Amounts reclassified from accumulated other comprehensive loss to net income	(1.1)
Other comprehensive income	43.6	33.6
Ending balance	(390.2)
Unrealized losses on available-for-sale securities
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	(0.6)
Other comprehensive income (loss) before reclassifications	(1.2)
Amounts reclassified from accumulated other comprehensive loss to net income	0.0
Other comprehensive income	(1.2)	(0.4)
Ending balance	(1.8)
Gains (Losses) on Cash Flow Hedges
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	24.6
Other comprehensive income (loss) before reclassifications	(6.0)
Amounts reclassified from accumulated other comprehensive loss to net income	(0.5)
Other comprehensive income	(6.5)	10.7
Ending balance	18.1
AOCI Attributable to Parent
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	(700.5)	(907.9)
Other comprehensive income (loss) before reclassifications	36.9
Amounts reclassified from accumulated other comprehensive loss to net income	(1.1)
Other comprehensive income	35.8	50.9
Ending balance	$ (664.7)	$ (857.0)