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Financial Instruments and Risk Management (Fair Value for Assets and Liabilities) (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
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Disclosure of fair value measurement of assets [line items] |  |
Financial assets | $ 3,396.5 | $ 3,272.2
Financial liabilities | (701.2) | (669.9)
Level 1 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Fair value, net asset (liability) | 22.8 | 7.8
Level 2 [member] | Recurring fair value measurement [member] |  |
Disclosure of fair value measurement of assets [line items] |  |
Fair value, net asset (liability) | 2.6 | (5.3)
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 liabilities | (0.7) | (0.1)
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)
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 liabilities |  | (4.7)
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 | 22.8 | $ 7.8
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 | $ 3.3 |

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- Definition Expiry date 2020-01-01: The amount of resources: (a) controlled by the entity as a result of past events; and (b) from which future economic benefits are expected to flow to the entity. Effective 2020-01-01: The amount of a present economic resource controlled by the entity as a result of past events. Economic resource is a right that has the potential to produce economic benefits. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 13 -IssueDate 2019-01-01 -Paragraph 93 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2019-en-r&anchor=para_93_a&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2019-01-01 -Paragraph 28 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2019-en-r&anchor=para_28_c&doctype=Standard -URIDate 2019-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 13 -IssueDate 2019-01-01 -Paragraph 93 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2019-en-r&anchor=para_93_b&doctype=Standard -URIDate 2019-03-27 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 13 -IssueDate 2019-01-01 -Paragraph 93 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2019-en-r&anchor=para_93_e&doctype=Standard -URIDate 2019-03-27 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_55&doctype=Standard -URIDate 2019-03-27 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2019-01-01 -Paragraph 23 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2019-en-r&anchor=para_23&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition Expiry date 2020-01-01: The amount of present obligations of the entity arising from past events, the settlement of which is expected to result in an outflow from the entity of resources embodying economic benefits. Effective 2020-01-01: The amount of a present obligation of the entity to transfer an economic resource as a result of past events. Economic resource is a right that has the potential to produce economic benefits. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 13 -IssueDate 2019-01-01 -Paragraph 93 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2019-en-r&anchor=para_93_a&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 13 -IssueDate 2019-01-01 -Paragraph 93 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2019-en-r&anchor=para_93_b&doctype=Standard -URIDate 2019-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 13 -IssueDate 2019-01-01 -Paragraph 93 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2019-en-r&anchor=para_93_e&doctype=Standard -URIDate 2019-03-27 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2019-01-01 -Paragraph 28 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2019-en-r&anchor=para_28_d&doctype=Standard -URIDate 2019-03-27 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2019-01-01 -Paragraph 23 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2019-en-r&anchor=para_23&doctype=Standard -URIDate 2019-03-27 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_55&doctype=Standard -URIDate 2019-03-27 + Details
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