Accounts receivable - Credit Quality of Finance Receivables (Details) $ in Millions	Oct. 31, 2020 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
Total at amortized cost	$ 54.2
Near Prime
Financing Receivable, Credit Quality Indicator [Line Items]
Total at amortized cost	26.4
Subprime
Financing Receivable, Credit Quality Indicator [Line Items]
Total at amortized cost	21.8
Deep Subprime
Financing Receivable, Credit Quality Indicator [Line Items]
Total at amortized cost	$ 6.0