PENSION AND OTHER POST-EMPLOYMENT BENEFITS - Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2020 USD ($)
Pension
Estimated Future Benefit Payments
2021	$ 579
2022	583
2023	598
2024	601
2025	610
Years 2026-2030	3,129
OPEB
Estimated Future Benefit Payments
2021	49
2022	47
2023	46
2024	45
2025	44
Years 2026-2030	197
Subsidy Receipts
2021	(1)
2022	(1)
2023	(1)
2024	(1)
2025	(1)
Years 2026-2030	$ (2)

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