Receivables and Revenue Recognition - Receivables (Details) - USD ($) $ in Millions	Jul. 31, 2018	Jan. 31, 2018	Jul. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit receivables	$ 64.4		$ 63.0
Credit receivables, current (as a percentage)	97.00%		96.00%
Allowance for doubtful accounts for estimated losses associated with the credit receivables	$ 1.1		$ 1.1
Accounts receivable allowances	28.8	$ 17.2	11.2
Prepaid expenses and other current assets	256.4	$ 207.4	$ 218.3
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Prepaid expenses and other current assets	$ 13.8