PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Funded Status of Our Plans (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 3,719	$ 4,930	$ 5,514
Projected benefit obligations	(4,260)	(5,263)	(6,795)
Funded status	(541)	(333)
Noncurrent assets	47	74
Current liabilities	(19)	(18)
Noncurrent liabilities	(569)	(389)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19	18	0
Projected benefit obligations	(151)	(166)	$ (200)
Funded status	(132)	(148)
Noncurrent assets	0	0
Current liabilities	(8)	(10)
Noncurrent liabilities	$ (124)	$ (138)

Amount of asset, recognized in statement of financial position, for overfunded defined benefit pension and other postretirement plans.

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Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as current.

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Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as noncurrent.

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