Hedging Instruments - Information on Location and Amounts of Derivative Gains and Losses in Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on hedging instruments		$ 4.3	$ (4.9)	$ (2.9)	$ (15.2)
Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on hedging instruments		4.3	(4.9)	(2.9)	(15.2)
Gain (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)		5.1	(3.6)	7.4	(12.5)
Cash Flow Hedging [Member] | Foreign exchange forward contracts [Member] | Cost of sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on hedging instruments	[1]	4.6	(0.6)	6.4	(3.8)
Gain (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)	[1]	0.7	(0.9)	2.3	(3.7)
Cash Flow Hedging [Member] | Precious metal collars [Member] | Cost of sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on hedging instruments	[1]	0.0	0.0	0.0	0.1
Gain (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)	[1]	0.2	0.1	0.3	0.1
Cash Flow Hedging [Member] | Precious metal forward contracts [Member] | Cost of sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on hedging instruments	[1]	(6.6)	(3.0)	(12.2)	(2.7)
Gain (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)	[1]	0.0	(0.3)	0.4	(1.2)
Cash Flow Hedging [Member] | Cross-currency swaps [Member] | Other (income) expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on hedging instruments	[2]	6.3	(1.3)	2.9	(8.8)
Gain (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)	[2]	4.5	(2.1)	5.1	(7.0)
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Interest expense and financing costs [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on hedging instruments	[3]	0.0	0.0	0.0	0.0
Gain (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)	[3]	$ (0.3)	$ (0.4)	$ (0.7)	$ (0.7)

[1] The gain or loss recognized in earnings is included within Cost of sales.

[2] The gain or loss recognized in earnings is included within Other (income) expense, net.

[3] The gain or loss recognized in earnings is included within Interest expense and financing costs.