Credit losses Credit losses (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($) country	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)
Valuation Allowance [Line Items]
Number of Countries in which Entity Operates | country	100
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for doubtful accounts, beginning balance	$ 30.2
Retained earnings	455.2		$ 457.4
Provision for uncollectible accounts receivable(a)	13.1
Write-offs less recoveries	(1.4)
Foreign currency exchange effects	(0.7)
Allowance for doubtful accounts, ending balance	43.5
Internal Loss AR Rebuild
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Provision for uncollectible accounts receivable(a)	10.6
Allowance for doubtful accounts, ending balance	$ 21.6
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Retained earnings		$ 2.3