Summary of Significant Accounting Policies Receivables and Financing Arrangements (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jul. 31, 2015	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan impairment charges	$ 12.6	$ 28.3	$ 9.6	$ 12.6	$ 37.9	$ 0.0
Consumer Credit Card Financing Receivables	$ 71.9	$ 75.2		$ 71.9	$ 75.2
Consumer Credit Card Financing Receivables Percentage Current	97.00%	97.00%		97.00%	97.00%
Consumer Credit Card Financing Receivable Allowance For Credit Losses	$ 1.1	$ 1.0		$ 1.1	$ 1.0
Financing Receivables Gross Current	4.6	2.1		4.6	2.1
Financing Receivables Gross Non Current	4.4	18.9		4.4	18.9
Koidu Limited [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	43.8			43.8
Loan impairment charges				4.2	37.9
Loans and Leases Receivable, Net Amount	$ 1.7	$ 5.9		1.7	$ 5.9
Other Diamond Mining and Exploration Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan impairment charges				$ 8.4