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Ghana Expected Credit Loss (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Disclosure of impairment loss and reversal of impairment loss [line items]      
Total expected credit loss $ (41.1) $ (29.0) $ 0.0
Ghana expected credit loss - loan advanced to contractor      
Disclosure of impairment loss and reversal of impairment loss [line items]      
Total expected credit loss (41.1) 0.0 0.0
Tarkwa expected credit loss - receivable      
Disclosure of impairment loss and reversal of impairment loss [line items]      
Total expected credit loss $ 0.0 $ (29.0) $ 0.0