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ACCOUNTING POLICIES (Employee liabilities) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of terms and conditions of share-based payment arrangement [line items]    
Deferred compensation share-based arrangements, liability $ 30.8 $ 23.4
Stock granted, value $ 30.3 $ 24.1
Incentive Retention Program | Capital Units    
Disclosure of terms and conditions of share-based payment arrangement [line items]    
Vesting period (years) 4 years  
Redemption, period (years) 10 years  
Early redemption, period (years) 7 years