Accumulated other comprehensive income (loss) - Reclasses Out Of AOCI (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	$ 366.7	$ 369.8	$ 252.6	$ 302.6	$ 225.1	$ 202.5	$ 252.6	$ 202.5
Other comprehensive loss	(33.1)	(39.6)	49.4	(24.4)	49.5	(42.8)	(23.3)	(17.7)
Acquisitions of noncontrolling interests	(7.8)
Ending balance	319.2	366.7	369.8	249.0	302.6	225.1	319.2	249.0
Benefit Plan Adjustments
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance			(474.0)				(474.0)
Other comprehensive income (loss) before reclassifications							0.7
Amounts reclassified from accumulated other comprehensive loss to net income							22.2
Other comprehensive loss	6.8			16.6			22.9	26.2
Ending balance	(451.1)						(451.1)
Foreign Currency Translation Adjustments
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance			(425.7)				(425.7)
Other comprehensive income (loss) before reclassifications							(60.7)
Amounts reclassified from accumulated other comprehensive loss to net income							(3.4)
Other comprehensive loss	(45.2)			(41.8)			(64.1)	(50.2)
Acquisitions of noncontrolling interests							0.1
Ending balance	(489.7)						(489.7)
Unrealized losses on available-for-sale securities
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance			(0.1)				(0.1)
Other comprehensive income (loss) before reclassifications							(1.0)
Amounts reclassified from accumulated other comprehensive loss to net income							0.0
Other comprehensive loss	(0.2)						(1.0)
Ending balance	(1.1)						(1.1)
Gains (Losses) on Cash Flow Hedges
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance			(8.1)				(8.1)
Other comprehensive income (loss) before reclassifications							21.3
Amounts reclassified from accumulated other comprehensive loss to net income							8.1
Other comprehensive loss	9.5			2.1			29.4	9.4
Ending balance	21.3						21.3
AOCI Attributable to Parent
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	(891.6)	(857.0)	(907.9)	(991.5)	(1,040.7)	(1,000.0)	(907.9)	(1,000.0)
Other comprehensive income (loss) before reclassifications							(39.7)
Amounts reclassified from accumulated other comprehensive loss to net income							26.9
Other comprehensive loss	(29.1)	(34.6)	50.9	(23.1)	49.2	(40.7)	(12.8)	(14.6)
Acquisitions of noncontrolling interests	0.1						0.1
Ending balance	$ (920.6)	$ (891.6)	$ (857.0)	$ (1,014.6)	$ (991.5)	$ (1,040.7)	$ (920.6)	$ (1,014.6)