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Financial Instruments and Risk Management (Market Price Risk) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) $ / oz
Disclosure of detailed information about hedged items [line items] |  |
Unrealized gains | $ (0.7) | $ 0.6
Market risk [member] |  |
Disclosure of detailed information about hedged items [line items] |  |
Potential percentage change in value | 1000.00% |
Impact on other comprehensive income | $ 4.3 | 2.1
Gold Options [Member] | Market risk [member] |  |
Disclosure of detailed information about hedged items [line items] |  |
Potential percentage change in value | 10.00% |
Impact on pre-tax earnings | $ 73.8 | $ 66.6
Bottom of range [member] | Gold Options [Member] | Market risk [member] |  |
Disclosure of detailed information about hedged items [line items] |  |
Average realized price per ounce | $ / oz |  | 1,474
Top of range [member] | Gold Options [Member] | Market risk [member] |  |
Disclosure of detailed information about hedged items [line items] |  |
Average realized price per ounce | $ / oz |  | 2,067

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