Receivables and Financing Arrangements (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Apr. 30, 2017	Jul. 31, 2017	Jul. 31, 2016	Jan. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer Credit Card Financing Receivables		$ 63.0	$ 70.9
Consumer Credit Card Financing Receivables Percentage Current		96.00%	97.00%
Consumer Credit Card Financing Receivable Allowance For Credit Losses		$ 1.1	$ 1.0
Financing Receivables Gross Current		1.5	3.0
Financing Receivables Net Non Current		3.4	19.2
Proceeds from sale of notes receivable		$ 1.7	0.0
Koidu Limited [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross				$ 43.8
Provision for Loan and Lease Losses				4.2
Loans and Leases Receivable, Net Amount			$ 5.9	1.7
Proceeds from sale of notes receivable	$ 1.7
Other Diamond Mining and Exploration Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Loan and Lease Losses				$ 8.4