FAIR VALUE MEASUREMENTS - Investments Held in Trusts (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Abstract]
Short-term cash investments	$ 9	$ 751
Short-term investments held-for-sale		747
Debt securities held-for-sale		135
Debt Securities
Debt Securities, Available-for-sale [Abstract]
Cost Basis	275	403
Unrealized Gains	7	9
Unrealized Losses	(6)	(11)
Fair Value	$ 276	$ 401

Cash and Cash Equivalents, Held-for-Sale, Fair Value Disclosure

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Debt Securities, Held-for-sale

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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