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Financial Instruments and Risk Management (Contractual Commitments) (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
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Disclosure of detailed information about financial instruments [abstract] |  |
Operating and financing leases, less than 1 year | $ 1.2 |
Operating and financing leases, 2-3 years | 0.7 |
Operating and financing leases, 4-5 years | 0.7 |
Operating and financing leases, more than 5 years | 0.6 |
Operating and financing leases, total | 3.2 |
Accounts payable and accrued liabilities, less than 1 year | 127.3 | $ 131.9
Accounts payable and accrued liabilities, 2-3 years | 0.0 |
Accounts payable and accrued liabilities, 4-5 years | 0.0 |
Accounts payable and accrued liabilities, more than 5 years | 0.0 |
Accounts payable and accrued liabilities, total | 127.3 |
Decommissioning liability, less than 1 year | 2.0 |
Decommissioning liability, 2-3 years | 2.1 |
Decommissioning liability, 4-5 years | 0.0 |
Decommissioning liability, more than 5 years | 62.0 |
Decommissioning liability, total | 66.1 |
Contract mining, less than 1 year | 24.8 |
Contract mining, 2-3 years | 50.6 |
Contract mining, 4-5 years | 3.5 |
Contract mining, more than 5 years | 0.0 |
Contract mining, total | 78.9 |
Capital commitments, less than 1 year | 44.0 |
Capital commitments, 2-3 years | 0.0 |
Capital commitments, 4-5 years | 0.0 |
Capital commitments, more than 5 years | 0.0 |
Capital commitments, total | 44.0 |
Contractual obligation, less than 1 year | 199.3 |
Contractual obligation, 2-3 years | 53.4 |
Contractual obligation, 4-5 years | 4.2 |
Contractual obligation, more than 5 years | 62.6 |
Contractual obligation, total | $ 319.5 |

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