Annual report pursuant to Section 13 and 15(d)

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Narrative) (Details)

v3.8.0.1
PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Narrative) (Details) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]    
401(k) contribution match $ 0.50  
Minimum participants percentage 15.00%  
Defined Benefit Plan, Accumulated Benefit Obligation $ 963,000,000 $ 922,000,000
Reserve for investment commitments $ 52,700,000  
Structured Finance [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Redemption request notice period, days 90 days  
Real Estate [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Redemption request notice period, days 45 days  
Withdrawal request notice period, days 65 days  
Pension Benefits [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Decrease in Projected Benefit Obligation due to Market Conditions $ 46,100,000  
Reduction in net periodic benefit expense 8,200,000  
Increase in Projected Benefit Obligation due to new mortality tables $ 6,100,000 $ 13,100,000
Percentage Increase in Projected Benefit Obligation due to new mortality tables 0.60% 1.40%
Other Benefits [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant $ 4,600,000 $ 6,000,000
Decrease in Projected Benefit Obligation due to Market Conditions 12,600,000  
Reduction in net periodic benefit expense 1,800,000  
Increase in Projected Benefit Obligation due to new mortality tables $ 1,900,000 $ 4,900,000
Percentage Increase in Projected Benefit Obligation due to new mortality tables 0.70% 1.80%
Prior To Age65 [Member] | United States [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Annual limit on medical coverage for each participant $ 7,000  
Prior To Age65 [Member] | Minimum [Member] | Northshore [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Annual limit on medical coverage for each participant 4,020  
Prior To Age65 [Member] | Maximum [Member] | Northshore [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Annual limit on medical coverage for each participant $ 4,500