Hedging Instruments - Information on Location and Amounts of Derivative Gains and Losses in Consolidated Financial Statements (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI (effective portion)	$ (1.1)	$ (21.0)	$ 12.1
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI (effective portion)	(1.1)	(21.0)
Pre-tax gain (loss) reclassified from accumulated OCI into earnings (effective portion)	1.2	(13.0)
Cash Flow Hedging | Foreign Exchange Forward | Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI (effective portion)	5.8	(6.3)
Pre-tax gain (loss) reclassified from accumulated OCI into earnings (effective portion)	2.6	0.1
Cash Flow Hedging | Precious metal collars | Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI (effective portion)	0.0	1.0
Pre-tax gain (loss) reclassified from accumulated OCI into earnings (effective portion)	0.6	0.3
Cash Flow Hedging | Precious Metal Forward Contracts | Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI (effective portion)	(7.2)	4.2
Pre-tax gain (loss) reclassified from accumulated OCI into earnings (effective portion)	(1.0)	(0.9)
Cash Flow Hedging | Currency Swap | Other (income) expense
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI (effective portion)	0.3	(19.9)
Pre-tax gain (loss) reclassified from accumulated OCI into earnings (effective portion)	0.4	(11.1)
Cash Flow Hedging | Interest Rate Swap | Interest expense and financing costs
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI (effective portion)	0.0	0.0
Pre-tax gain (loss) reclassified from accumulated OCI into earnings (effective portion)	$ (1.4)	$ (1.4)