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Fair value of financial instruments (Details) $ in Millions	3 Months Ended		9 Months Ended
Fair value of financial instruments (Details) $ in Millions	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2021 derivative_instrument	Dec. 31, 2020 USD ($)	Mar. 31, 2019 derivative_instrument
Debt Securities, Available-for-sale [Line Items]
Other operating income (expense)	$ 1.8	$ 9.8	$ 5.2	$ 18.4
Foreign currency transaction gains (losses)			(6.6)	(5.3)
Interest expense	(27.6)	(27.1)	(83.0)	(70.3)
Not Designated as Hedging Instrument \| Foreign Exchange Contract
Debt Securities, Available-for-sale [Line Items]
Notional value of nonderivative instruments			$ 544.0
Weighted average maturity			1 month
Not Designated as Hedging Instrument \| Foreign Exchange Contract \| Other operating income (expense)
Debt Securities, Available-for-sale [Line Items]
Gain (loss) on foreign currency contract	6.3	(3.4)	$ 14.5	0.5
Not Designated as Hedging Instrument \| Foreign Exchange Contract \| Nonoperating income (expense)
Debt Securities, Available-for-sale [Line Items]
Gain (loss) on foreign currency contract	0.0	(0.5)	0.0	(8.6)
Not Designated as Hedging Instrument \| Foreign Exchange Contract \| Level 2
Debt Securities, Available-for-sale [Line Items]
Fair value of derivative instruments	2.8		2.8			$ 2.4
Designated as Hedging Instrument \| Level 2
Debt Securities, Available-for-sale [Line Items]
Interest expense	(0.9)	(2.3)	(4.7)	(5.2)
Designated as Hedging Instrument \| Currency Swap
Debt Securities, Available-for-sale [Line Items]
Notional value of derivative instrument	81.0		$ 81.0
Weighted average maturity			1 year 4 months 24 days
Other operating income (expense)	(5.7)	(0.8)	$ (0.1)	(30.6)
Foreign currency transaction gains (losses)	(5.7)	(0.8)	(0.1)	(30.6)
Interest expense	(0.3)	(0.5)	(1.1)	(1.5)
Foreign currency derivative instrument gains (losses)	5.4	0.3	(1.0)	29.1
Designated as Hedging Instrument \| Currency Swap \| Level 2
Debt Securities, Available-for-sale [Line Items]
Fair value of contract, asset position	26.4		26.4			23.6
Designated as Hedging Instrument \| $400 million interest rate swap
Debt Securities, Available-for-sale [Line Items]
Notional value of derivative instrument	400.0		$ 400.0
Weighted average maturity			1 year 2 months 12 days
Number of instruments held \| derivative_instrument							10
Designated as Hedging Instrument \| $400 million interest rate swap \| Level 2
Debt Securities, Available-for-sale [Line Items]
Interest expense	(2.4)	(2.3)	$ (7.3)	(5.2)
Fair value of swap, net	20.0		20.0			29.0
Designated as Hedging Instrument \| $400 cross currency swap
Debt Securities, Available-for-sale [Line Items]
Notional value of derivative instrument	400.0		$ 400.0
Weighted average maturity			6 years 9 months 18 days
Number of instruments held \| derivative_instrument					10
Designated as Hedging Instrument \| $400 cross currency swap \| Level 2
Debt Securities, Available-for-sale [Line Items]
Fair value of contract, asset position	18.2		$ 18.2
Interest expense	(1.5)	$ 0.0	(2.6)	$ 0.0
Prepaid expenses and other \| Not Designated as Hedging Instrument \| Foreign Exchange Contract \| Level 2
Debt Securities, Available-for-sale [Line Items]
Fair value of derivative instruments	5.4		5.4			3.5
Prepaid expenses and other \| Designated as Hedging Instrument \| Currency Swap \| Level 2
Debt Securities, Available-for-sale [Line Items]
Fair value of contract, asset position	5.1		5.1			3.2
Prepaid expenses and other \| Designated as Hedging Instrument \| $400 cross currency swap \| Level 2
Debt Securities, Available-for-sale [Line Items]
Fair value of contract, asset position	6.0		6.0
Accrued liabilities \| Not Designated as Hedging Instrument \| Foreign Exchange Contract \| Level 2
Debt Securities, Available-for-sale [Line Items]
Fair value of derivative instruments	2.6		2.6			1.1
Accrued liabilities \| Designated as Hedging Instrument \| $400 million interest rate swap \| Level 2
Debt Securities, Available-for-sale [Line Items]
Fair value of swap, liability position	9.7		9.7			9.7
Other assets \| Designated as Hedging Instrument \| Currency Swap \| Level 2
Debt Securities, Available-for-sale [Line Items]
Fair value of contract, asset position	21.3		21.3			20.4
Other assets \| Designated as Hedging Instrument \| $400 cross currency swap \| Level 2
Debt Securities, Available-for-sale [Line Items]
Fair value of contract, asset position	12.2		12.2
Other liabilities \| Designated as Hedging Instrument \| $400 million interest rate swap \| Level 2
Debt Securities, Available-for-sale [Line Items]
Fair value of swap, liability position	10.3		10.3			19.3
Six hundred million senior unsecured notes
Debt Securities, Available-for-sale [Line Items]
Carrying value	600.0		600.0			600.0
Six hundred million senior unsecured notes \| Level 3
Debt Securities, Available-for-sale [Line Items]
Fair value	631.1		631.1			640.9
Four hundred million senior unsecured notes
Debt Securities, Available-for-sale [Line Items]
Carrying value	400.0		400.0			400.0
Four hundred million senior unsecured notes \| Level 3
Debt Securities, Available-for-sale [Line Items]
Fair value	$ 419.3		$ 419.3			$ 426.8