Fair Value of Financial Instruments - Financial Assets and Liabilities Carried at Fair Value (Details) - USD ($) $ in Millions		Oct. 31, 2019	Apr. 30, 2019	Oct. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets, fair value		$ 93.1	$ 106.9	$ 56.5
Total financial liabilities, fair value		9.6	27.4	21.9
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets, fair value		78.3	99.0	48.7
Total financial liabilities, fair value		0.0	0.0	0.0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets, fair value		14.8	7.9	7.8
Total financial liabilities, fair value		9.6	27.4	21.9
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets, fair value		0.0	0.0	0.0
Total financial liabilities, fair value		0.0	0.0	0.0
Bank Time Deposits | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	[1]	40.0	62.7	12.8
Bank Time Deposits | Level 1 | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	[1]	40.0	62.7	12.8
Bank Time Deposits | Level 2 | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	[1]	0.0	0.0	0.0
Bank Time Deposits | Level 3 | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	[1]	0.0	0.0	0.0
Marketable Securities | Other assets, net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	[2]	38.3	36.3	35.9
Marketable Securities | Level 1 | Other assets, net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	[2]	38.3	36.3	35.9
Marketable Securities | Level 2 | Other assets, net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	[2]	0.0	0.0	0.0
Marketable Securities | Level 3 | Other assets, net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	[2]	0.0	0.0	0.0
Precious Metal Forward Contracts | Prepaid expenses and other current assets | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	[3]	9.6	5.2	0.4
Precious Metal Forward Contracts | Level 1 | Prepaid expenses and other current assets | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	[3]	0.0	0.0	0.0
Precious Metal Forward Contracts | Level 2 | Prepaid expenses and other current assets | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	[3]	9.6	5.2	0.4
Precious Metal Forward Contracts | Level 3 | Prepaid expenses and other current assets | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	[3]	0.0	0.0	0.0
Foreign Exchange Forward | Prepaid expenses and other current assets | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	[3]	2.4	1.8	5.6
Foreign Exchange Forward | Prepaid expenses and other current assets | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	[3]	1.5	0.9	1.8
Foreign Exchange Forward | Level 1 | Prepaid expenses and other current assets | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	[3]	0.0	0.0	0.0
Foreign Exchange Forward | Level 1 | Prepaid expenses and other current assets | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	[3]	0.0	0.0	0.0
Foreign Exchange Forward | Level 2 | Prepaid expenses and other current assets | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	[3]	2.4	1.8	5.6
Foreign Exchange Forward | Level 2 | Prepaid expenses and other current assets | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	[3]	1.5	0.9	1.8
Foreign Exchange Forward | Level 3 | Prepaid expenses and other current assets | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	[3]	0.0	0.0	0.0
Foreign Exchange Forward | Level 3 | Prepaid expenses and other current assets | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	[3]	0.0	0.0	0.0
Currency Swap | Prepaid expenses and other current assets | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value		1.3
Currency Swap | Level 1 | Prepaid expenses and other current assets | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value		0.0
Currency Swap | Level 2 | Prepaid expenses and other current assets | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value		1.3
Currency Swap | Level 3 | Prepaid expenses and other current assets | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value		0.0
Precious Metal Forward Contracts | Accounts Payable and Accrued Liabilities | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	1.0	2.7	6.4
Precious Metal Forward Contracts | Level 1 | Accounts Payable and Accrued Liabilities | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	0.0	0.0	0.0
Precious Metal Forward Contracts | Level 2 | Accounts Payable and Accrued Liabilities | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	1.0	2.7	6.4
Precious Metal Forward Contracts | Level 3 | Accounts Payable and Accrued Liabilities | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	0.0	0.0	0.0
Foreign Exchange Forward | Accounts Payable and Accrued Liabilities | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	0.6	2.1	0.1
Foreign Exchange Forward | Accounts Payable and Accrued Liabilities | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	3.8	2.7	0.9
Foreign Exchange Forward | Level 1 | Accounts Payable and Accrued Liabilities | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	0.0	0.0	0.0
Foreign Exchange Forward | Level 1 | Accounts Payable and Accrued Liabilities | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	0.0	0.0	0.0
Foreign Exchange Forward | Level 2 | Accounts Payable and Accrued Liabilities | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	0.6	2.1	0.1
Foreign Exchange Forward | Level 2 | Accounts Payable and Accrued Liabilities | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	3.8	2.7	0.9
Foreign Exchange Forward | Level 3 | Accounts Payable and Accrued Liabilities | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	0.0	0.0	0.0
Foreign Exchange Forward | Level 3 | Accounts Payable and Accrued Liabilities | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	0.0	0.0	0.0
Currency Swap | Accounts Payable and Accrued Liabilities | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	4.2	19.9	14.5
Currency Swap | Level 1 | Accounts Payable and Accrued Liabilities | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	0.0	0.0	0.0
Currency Swap | Level 2 | Accounts Payable and Accrued Liabilities | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	4.2	19.9	14.5
Currency Swap | Level 3 | Accounts Payable and Accrued Liabilities | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	[4]	$ 0.0	$ 0.0	$ 0.0

[1] Included within Short-term investments.

[2] Included within Other assets, net.

[3] Included within Prepaid expenses and other current assets or Other assets, net based on the maturity of the contract.

[4] Included within Accounts payable and accrued liabilities or Other long-term liabilities based on the maturity of the contract.