Annual report pursuant to Section 13 and 15(d)

PENSIONS AND OTHER POSTRETIREMENT BENEFITS - Target Allocation and Actual Asset Allocations for Pension and VEBA Plan Assets (Details)

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PENSIONS AND OTHER POSTRETIREMENT BENEFITS - Target Allocation and Actual Asset Allocations for Pension and VEBA Plan Assets (Details)
Dec. 31, 2020
Dec. 31, 2019
Pension Plan [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 100.00% 100.00%
Target Allocation, Percentage, Next Fiscal Year 100.00%  
Pension Plan [Member] | Equity Securities [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 51.80% 44.00%
Target Allocation, Percentage, Next Fiscal Year 41.30%  
Pension Plan [Member] | Fixed Income Investments [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 33.80% 27.60%
Target Allocation, Percentage, Next Fiscal Year 39.70%  
Pension Plan [Member] | Hedge Funds [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 2.20% 5.40%
Target Allocation, Percentage, Next Fiscal Year 5.00%  
Pension Plan [Member] | Private Equity Funds [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 2.10% 6.60%
Target Allocation, Percentage, Next Fiscal Year 2.20%  
Pension Plan [Member] | Structured Finance [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 5.00% 7.00%
Target Allocation, Percentage, Next Fiscal Year 5.20%  
Pension Plan [Member] | Real Estate [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 3.30% 9.40%
Target Allocation, Percentage, Next Fiscal Year 5.20%  
Pension Plan [Member] | Absolute return fixed income    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 1.80% 0.00%
Target Allocation, Percentage, Next Fiscal Year 1.40%  
Other Postretirement Benefits Plan [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 100.00% 100.00%
Target Allocation, Percentage, Next Fiscal Year 100.00%  
Other Postretirement Benefits Plan [Member] | Equity Securities [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 22.20% 7.20%
Target Allocation, Percentage, Next Fiscal Year 20.30%  
Other Postretirement Benefits Plan [Member] | Fixed Income Investments [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 66.40% 79.80%
Target Allocation, Percentage, Next Fiscal Year 69.60%  
Other Postretirement Benefits Plan [Member] | Hedge Funds [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 1.80% 4.80%
Target Allocation, Percentage, Next Fiscal Year 1.10%  
Other Postretirement Benefits Plan [Member] | Private Equity Funds [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 0.40% 0.70%
Target Allocation, Percentage, Next Fiscal Year 1.40%  
Other Postretirement Benefits Plan [Member] | Structured Finance [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 0.90% 2.10%
Target Allocation, Percentage, Next Fiscal Year 1.00%  
Other Postretirement Benefits Plan [Member] | Real Estate [Member]    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 1.80% 5.40%
Target Allocation, Percentage, Next Fiscal Year 1.10%  
Other Postretirement Benefits Plan [Member] | Absolute return fixed income    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Percentage of Plan Assets 6.50% 0.00%
Target Allocation, Percentage, Next Fiscal Year 5.50%