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FREIGHT RECEIVABLES - Additional Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of financial assets that are either past due or impaired [line items]        
Receivables individually determined to be impaired $ 89.9 $ 86.0 $ 71.3  
Later than one year [member]        
Disclosure of financial assets that are either past due or impaired [line items]        
Percentage of expected credit loss 100.00%      
Maximum | Later than six months and not later than one year [member]        
Disclosure of financial assets that are either past due or impaired [line items]        
Percentage of expected credit loss 100.00%      
Minimum | Later than six months and not later than one year [member]        
Disclosure of financial assets that are either past due or impaired [line items]        
Percentage of expected credit loss 25.00%      
Accumulated impairment        
Disclosure of financial assets that are either past due or impaired [line items]        
Receivables individually determined to be impaired $ 3.7 1.7 1.3 $ 2.6
Financial assets individually assessed for credit losses | Accumulated impairment        
Disclosure of financial assets that are either past due or impaired [line items]        
Freight receivables included receivables 0.0 0.0 0.0  
Receivables individually determined to be impaired $ 0.0 $ 0.0 $ 0.0