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PENSION AND OTHER POST-EMPLOYMENT BENEFITS - Narrative (Details) $ in Millions |  |  |  | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | ---
May 12, 2023 USD ($) | Apr. 30, 2023 | Dec. 31, 2022 | Jun. 30, 2023 USD ($) | Jun. 30, 2022 USD ($) | Jun. 30, 2023 USD ($) | Jun. 30, 2022 USD ($) | Dec. 31, 2023 | May 09, 2023 employee
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |
Percent of eligible employees that accepted the voluntary retirement program |  |  |  |  |  |  |  |  | 0.65
Number of employees | employee |  |  |  |  |  |  |  |  | 450
Number of separated employees | employee |  |  |  |  |  |  |  |  | 90
Defined benefit plan, assumptions used calculating benefit obligation, increase (decrease) in discount rate |  |  |  | 0.29% |  |  |  |  |
Pension |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |
Voluntary cash contribution | $ 750 |  |  |  |  |  |  |  |
Discount rate |  | 4.94% | 5.23% |  |  |  |  |  |
Pension and OPEB mark-to-market adjustment |  |  |  | $ (59) | $ 0 | $ (59) | $ 0 |  |
Voluntary contribution, percentage |  | 7.70% |  |  |  |  |  |  |
Estimated return |  | 2.67% |  |  |  | 800.00% |  |  |
Pension | Forecast |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |
Discount rate |  |  |  |  |  |  |  | 8.00% |
OPEB |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |
Discount rate |  |  | 5.16% |  |  |  |  |  |
Pension and OPEB mark-to-market adjustment |  |  |  | 0 | $ 0 | $ 0 | $ 0 |  |
Estimated return |  |  |  |  |  | 7.00% |  |  |
Pension Mark-to-market Adjustment |  |  |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |  |  |
Net periodic benefit cost, pre-tax |  |  |  | $ 47 |  |  |  |  |

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