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CAPITAL MANAGEMENT (Details) - USD ($)
$ in Millions
 12 Months Ended
Sep. 23, 2020
Jun. 27, 2019
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Disclosure of detailed information about borrowings [line items]          
Cash and cash equivalents     $ 544.9 $ 941.5 $ 830.6
Short-term investments     7.6 6.0  
Cash and cash equivalents including short-term investments     552.5 947.5  
Long-term debt     450.0 450.0  
Credit facility available for use     498.3 498.3  
Common shares     2,719.1 2,710.8  
Capital Management Liabilities And Equity     3,686.3 3,687.3  
Borrowing costs capitalised     31.4 24.5  
5.75% senior notes          
Disclosure of detailed information about borrowings [line items]          
Long-term debt $ 454.2   450.0 450.0  
Borrowing costs capitalised $ 7.5        
5.75% senior notes | Unamortized deferred transactions costs          
Disclosure of detailed information about borrowings [line items]          
Borrowing costs capitalised     6.3 7.2  
Equipment loans          
Disclosure of detailed information about borrowings [line items]          
Long-term debt     18.9 28.2  
Borrowing costs capitalised   $ 0.3      
Equipment loans | Unamortized deferred transactions costs          
Disclosure of detailed information about borrowings [line items]          
Borrowing costs capitalised     $ 0.2 $ 0.2