Contract assets and contract liabilities (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract assets - current	$ 53.0	$ 29.7
Contract assets - long-term	21.6	22.2
Deferred revenue - current	(288.6)	(294.4)
Deferred revenue - long-term	(147.4)	(157.2)
Deposit liabilities principally included in current deferred revenue	25.3	21.2
Revenue recognized that was included in deferred revenue at the beginning of the period	$ 287.9	$ 307.1

Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, classified as current.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130531-203044

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
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-Section 50
-Paragraph 8
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- Definition

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

+ References

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-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130531-203044

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as noncurrent.

+ References

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-Publisher FASB
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Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

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- Definition

The current portion, due within one year or one operating cycle, if longer, of deposits held other than customer deposits.

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-Publisher FASB
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No definition available.

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