Accounts receivable - Rollforward of Allowance for Credit Losses (Details) $ in Millions	9 Months Ended
Oct. 31, 2020 USD ($)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at February 1, 2020	$ 0.0
Provision for credit losses	14.6
Write-offs	0.0
Recoveries	0.0
Balance at October 31, 2020	$ 14.6

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of increase in allowance for credit loss on financing receivable from recovery.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of writeoff of financing receivable, charged against allowance for credit loss.

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- Definition

Amount of credit loss expense (reversal of expense) for financing receivable.

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