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Financial Instruments and Risk Management (Fair Value for Assets and Liabilities) (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Disclosure of fair value measurement of assets [line items] |  |
Financial assets | $ 3,265.2 | $ 3,320.3
Financial liabilities | (662.9) | (639.1)
Level 1 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Fair value, net asset (liability) | 7.8 | 35.7
Level 2 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Fair value, net asset (liability) | (5.3) | 5.5
Fair value through profit or loss | Share Purchase Warrants [Member] | Level 1 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial liabilities | 0.0 | (0.1)
Fair value through profit or loss | Share Purchase Warrants [Member] | Level 2 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial liabilities | 0.0 | 0.0
Fair value through profit or loss | Currency Derivative Instruments [Member] | Level 1 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial liabilities | 0.0 | 0.0
Fair value through profit or loss | Currency Derivative Instruments [Member] | Level 2 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial liabilities | (0.1) | 0.0
Fair value through profit or loss | Gold Options [Member] | Level 1 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial assets | 0.0 | 0.0
Fair value through profit or loss | Gold Options [Member] | Level 2 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial assets | 0.0 | 0.5
Fair value through OCI | Currency Derivative Instruments [Member] | Level 1 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial liabilities | 0.0 | 0.0
Fair value through OCI | Currency Derivative Instruments [Member] | Level 2 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial liabilities | (4.7) | 0.0
Fair value through OCI | Fuel Options [Member] | Level 1 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial liabilities | 0.0 | 0.0
Fair value through OCI | Fuel Options [Member] | Level 2 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial liabilities | (0.5) | 0.0
Fair value through OCI | Trading securities [member] | Level 1 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial assets | 7.8 | 35.8
Fair value through OCI | Trading securities [member] | Level 2 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial assets | 0.0 | 0.0
Fair value through OCI | Currency Hedging Derivative Instruments [Member] | Level 1 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial assets | 0.0 | 0.0
Fair value through OCI | Currency Hedging Derivative Instruments [Member] | Level 2 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Financial assets | $ 0.0 | $ 5.0

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