Receivables and allowance for expected credit losses (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Credit Loss [Abstract]
Receivables past due 90 days or more	$ 48.9	$ 46.7	$ 56.0

Amount of financing receivable 90 days or more past due and still accruing.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919258-210447

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-Section 55
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-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922355-210448

Name:	us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant