AVAILABLE-FOR-SALE DEBT SECURITIES - Summary of Available-for-Sale Debt Securities at Estimated Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Available-for-Sale Debt Securities
Amortized Cost	$ 2,523	$ 2,023
Gross Unrealized Gains	1	3
Gross Unrealized Losses	(1)	0
Estimated Fair Value	2,523	2,026
U.S. treasury securities
Available-for-Sale Debt Securities
Amortized Cost	413	308
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	0
Estimated Fair Value	413	309
Certificates of deposit
Available-for-Sale Debt Securities
Amortized Cost	387	216
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	387	216
Non-U.S. government securities
Available-for-Sale Debt Securities
Amortized Cost	49	43
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	49	43
Corporate debt securities
Available-for-Sale Debt Securities
Amortized Cost	1,262	1,140
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(1)	0
Estimated Fair Value	1,262	1,142
Residential mortgage and asset-backed securities
Available-for-Sale Debt Securities
Amortized Cost	412	316
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 412	$ 316

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).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

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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).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

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Amortized cost excluding accrued interest, after allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-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

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Amount excluding accrued interest, 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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