FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Fair Value Measurements on a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Investments:	$ 538	$ 451
Total	2,276	2,094
Fair Value Measurements on a Recurring Basis
Debt Securities, Available-for-sale [Line Items]
Cash equivalents:	25	13
Investments:	303	195
Restricted cash equivalents:	94	99
Restricted investments:	235	256
Total	657	563
Fair Value Measurements on a Recurring Basis \| Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Investments:	49	24
Fair Value Measurements on a Recurring Basis \| Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Investments:	137	93
Restricted investments:	30	35
Fair Value Measurements on a Recurring Basis \| U.S. government agencies and government-sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Investments:	2	5
Restricted investments:	15	23
Fair Value Measurements on a Recurring Basis \| U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Investments:	106	67
Restricted investments:	179	198
Fair Value Measurements on a Recurring Basis \| Certificate of deposit
Debt Securities, Available-for-sale [Line Items]
Restricted cash equivalents:	1
Restricted investments:	11
Fair Value Measurements on a Recurring Basis \| Other debt securities
Debt Securities, Available-for-sale [Line Items]
Investments:	9	6
Fair Value Measurements on a Recurring Basis \| Level 1
Debt Securities, Available-for-sale [Line Items]
Cash equivalents:	4	2
Investments:	0	0
Restricted cash equivalents:	93	99
Restricted investments:	0	0
Total	97	101
Fair Value Measurements on a Recurring Basis \| Level 1 \| Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Investments:	0	0
Fair Value Measurements on a Recurring Basis \| Level 1 \| Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Investments:	0	0
Restricted investments:	0	0
Fair Value Measurements on a Recurring Basis \| Level 1 \| U.S. government agencies and government-sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Investments:	0	0
Restricted investments:	0	0
Fair Value Measurements on a Recurring Basis \| Level 1 \| U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Investments:	0	0
Restricted investments:	0	0
Fair Value Measurements on a Recurring Basis \| Level 1 \| Certificate of deposit
Debt Securities, Available-for-sale [Line Items]
Restricted investments:	0
Fair Value Measurements on a Recurring Basis \| Level 1 \| Other debt securities
Debt Securities, Available-for-sale [Line Items]
Investments:	0	0
Fair Value Measurements on a Recurring Basis \| Level 2
Debt Securities, Available-for-sale [Line Items]
Cash equivalents:	21	11
Investments:	303	195
Restricted cash equivalents:	1	0
Restricted investments:	235	256
Total	560	462
Fair Value Measurements on a Recurring Basis \| Level 2 \| Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Investments:	49	24
Fair Value Measurements on a Recurring Basis \| Level 2 \| Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Investments:	137	93
Restricted investments:	30	35
Fair Value Measurements on a Recurring Basis \| Level 2 \| U.S. government agencies and government-sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Investments:	2	5
Restricted investments:	15	23
Fair Value Measurements on a Recurring Basis \| Level 2 \| U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Investments:	106	67
Restricted investments:	179	198
Fair Value Measurements on a Recurring Basis \| Level 2 \| Certificate of deposit
Debt Securities, Available-for-sale [Line Items]
Restricted investments:	11
Fair Value Measurements on a Recurring Basis \| Level 2 \| Other debt securities
Debt Securities, Available-for-sale [Line Items]
Investments:	9	6
Money market mutual funds \| Fair Value Measurements on a Recurring Basis
Debt Securities, Available-for-sale [Line Items]
Cash equivalents:	4	2
Money market mutual funds \| Fair Value Measurements on a Recurring Basis \| Level 1
Debt Securities, Available-for-sale [Line Items]
Cash equivalents:	4	2
Money market mutual funds \| Fair Value Measurements on a Recurring Basis \| Level 2
Debt Securities, Available-for-sale [Line Items]
Cash equivalents:	0	0
U.S. treasuries \| Fair Value Measurements on a Recurring Basis
Debt Securities, Available-for-sale [Line Items]
Cash equivalents:	21	11
U.S. treasuries \| Fair Value Measurements on a Recurring Basis \| Level 1
Debt Securities, Available-for-sale [Line Items]
Cash equivalents:	0	0
U.S. treasuries \| Fair Value Measurements on a Recurring Basis \| Level 2
Debt Securities, Available-for-sale [Line Items]
Cash equivalents:	21	$ 11
Certificate of deposit \| Fair Value Measurements on a Recurring Basis \| Level 1
Debt Securities, Available-for-sale [Line Items]
Restricted cash equivalents:	0
Certificate of deposit \| Fair Value Measurements on a Recurring Basis \| Level 2
Debt Securities, Available-for-sale [Line Items]
Restricted cash equivalents:	$ 1

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_CashEquivalentsAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Cash and investments whose use in whole or in part is restricted for the long-term, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

+ References

+ Details

Name:	us-gaap_RestrictedCashAndInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of cash equivalents restricted as to withdrawal or usage. Cash equivalents include, but are not limited to, 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.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(2))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 954
-SubTopic 210
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=120413173&loc=SL6242262-115580

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=123431023&loc=SL98516268-108586

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 954
-SubTopic 210
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=120413209&loc=SL6242269-115581

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(1)(a))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_RestrictedCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The aggregate value of all restricted investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 954
-SubTopic 210
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=120413173&loc=SL6242262-115580

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-12.6(c))
-URI http://asc.fasb.org/extlink&oid=122147990&loc=d3e611133-123010

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 954
-SubTopic 210
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=120413209&loc=SL6242269-115581

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-12B(Footnote 11(c)))
-URI http://asc.fasb.org/extlink&oid=122147990&loc=d3e611197-123010

+ Details

Name:	us-gaap_RestrictedInvestmentsAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_OtherDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CashAndCashEquivalentsAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CashAndCashEquivalentsAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CashAndCashEquivalentsAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: