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PENSIONS AND OTHER POSTRETIREMENT BENEFITS - Contributions (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Pension Plan [Member] |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Employer contributions | $ 50 | $ 16
Expected employer contributions, next fiscal year | 202 |
Other Postretirement Benefits Plan [Member] |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Employer contributions | 30 | 3
Expected employer contributions, next fiscal year | 128 |
Defined Benefit Plan, Plan Assets, Contributions by Employer | 25 | 4
Other Postretirement Benefits Plan [Member] | Veba Trust [Member] |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Expected employer contributions, next fiscal year | (16) |
Defined Benefit Plan, Plan Assets, Contributions by Employer | 0 | 0
Other Postretirement Benefits Plan [Member] | Direct Payments [Member] |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Expected employer contributions, next fiscal year | 144 |
Defined Benefit Plan, Plan Assets, Contributions by Employer | $ 25 | $ 4

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