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Mineral Property, Pland and Equipment (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2017
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | $ 1,918.2 |  |
Mineral property, plant and equipment | 1,918.2 |  | $ 2,753.4
Gross carrying amount [member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 2,678.1 | $ 2,502.3 |
Additions | 179.0 | 158.4 |
Acquisitions of new entities | 774.3 | 19.9 |
Transfers |  | 4.2 |
Disposals | (2.7) | (6.7) |
Mineral property, plant and equipment | 2,678.1 | 2,502.3 | 3,628.7
Accumulated depreciation, amortisation and impairment [member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 759.9 | 643.1 |
Amortization | 116.5 | 118.9 |
Disposals | (1.1) | (2.1) |
Mineral property, plant and equipment | 759.9 | 643.1 | 875.3
Plant and Equipment [Member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 710.2 |  |
Mineral property, plant and equipment | 710.2 |  | 769.1
Plant and Equipment [Member] | Gross carrying amount [member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 983.6 | 922.9 |
Additions | 66.4 | 67.4 |
Acquisitions of new entities | 55.7 | 0.0 |
Transfers |  | 0.0 |
Disposals | (2.7) | (6.7) |
Mineral property, plant and equipment | 983.6 | 922.9 | 1,103.0
Plant and Equipment [Member] | Accumulated depreciation, amortisation and impairment [member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 273.4 | 206.5 |
Amortization | 61.6 | 69.0 |
Disposals | (1.1) | (2.1) |
Mineral property, plant and equipment | 273.4 | 206.5 | 333.9
Mineral Property - Depletable [Member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 867.9 |  |
Mineral property, plant and equipment | 867.9 |  | 1,588.3
Mineral Property - Depletable [Member] | Gross carrying amount [member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 1,343.0 | 1,286.7 |
Additions | 56.7 | 56.3 |
Acquisitions of new entities | 718.6 | 0.0 |
Transfers |  | 0.0 |
Disposals | 0.0 | 0.0 |
Mineral property, plant and equipment | 1,343.0 | 1,286.7 | 2,118.3
Mineral Property - Depletable [Member] | Accumulated depreciation, amortisation and impairment [member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 475.1 | 425.2 |
Amortization | 54.9 | 49.9 |
Disposals | 0.0 | 0.0 |
Mineral property, plant and equipment | 475.1 | 425.2 | 530.0
Mineral Property - Non-Depletable [Member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 61.1 |  |
Mineral property, plant and equipment | 61.1 |  | 75.4
Mineral Property - Non-Depletable [Member] | Gross carrying amount [member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 66.2 | 48.4 |
Additions | 14.3 | 17.8 |
Acquisitions of new entities | 0.0 | 0.0 |
Transfers |  | 0.0 |
Disposals | 0.0 | 0.0 |
Mineral property, plant and equipment | 66.2 | 48.4 | 80.5
Mineral Property - Non-Depletable [Member] | Accumulated depreciation, amortisation and impairment [member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 5.1 | 5.1 |
Amortization | 0.0 | 0.0 |
Disposals | 0.0 | 0.0 |
Mineral property, plant and equipment | 5.1 | 5.1 | 5.1
Exploration and evaluation assets [member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 279.0 |  |
Mineral property, plant and equipment | 279.0 |  | 320.6
Exploration and evaluation assets [member] | Gross carrying amount [member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 285.3 | 244.3 |
Additions | 41.6 | 16.9 |
Acquisitions of new entities | 0.0 | 19.9 |
Transfers |  | 4.2 |
Disposals | 0.0 | 0.0 |
Mineral property, plant and equipment | 285.3 | 244.3 | 326.9
Exploration and evaluation assets [member] | Accumulated depreciation, amortisation and impairment [member] |  |  |
Reconciliation of changes in property, plant and equipment [abstract] |  |  |
Property, plant and equipment | 6.3 | 6.3 |
Amortization | 0.0 | 0.0 |
Disposals | 0.0 | 0.0 |
Mineral property, plant and equipment | $ 6.3 | $ 6.3 | $ 6.3

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