Annual report pursuant to Section 13 and 15(d)

BENEFIT PLANS (Asset Allocation Ranges and Actual Allocation, CRIP) (Details)

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BENEFIT PLANS (Asset Allocation Ranges and Actual Allocation, CRIP) (Details) - Other Benefits - Canada
Dec. 31, 2017
Dec. 31, 2016
Canadian Equities    
Defined Benefit Plan Disclosure [Line Items]    
Actual 35.20% 34.70%
International Equities (including U.S. Equities)    
Defined Benefit Plan Disclosure [Line Items]    
Actual 14.90% 14.90%
Fixed Income    
Defined Benefit Plan Disclosure [Line Items]    
Actual 49.10% 49.10%
Money Market    
Defined Benefit Plan Disclosure [Line Items]    
Actual 0.80% 1.30%
Minimum | Canadian Equities    
Defined Benefit Plan Disclosure [Line Items]    
Range 25.00%  
Minimum | International Equities (including U.S. Equities)    
Defined Benefit Plan Disclosure [Line Items]    
Range 0.00%  
Minimum | Fixed Income    
Defined Benefit Plan Disclosure [Line Items]    
Range 40.00%  
Minimum | Money Market    
Defined Benefit Plan Disclosure [Line Items]    
Range 0.00%  
Maximum | Canadian Equities    
Defined Benefit Plan Disclosure [Line Items]    
Range 50.00%  
Maximum | International Equities (including U.S. Equities)    
Defined Benefit Plan Disclosure [Line Items]    
Range 19.00%  
Maximum | Fixed Income    
Defined Benefit Plan Disclosure [Line Items]    
Range 60.00%  
Maximum | Money Market    
Defined Benefit Plan Disclosure [Line Items]    
Range 10.00%