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AVAILABLE-FOR-SALE DEBT SECURITIES - Summary of Available-for-Sale Debt Securities at Estimated Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Available-for-Sale Debt Securities
Amortized Cost	$ 2,478	$ 2,023
Gross Unrealized Gains	1	3
Gross Unrealized Losses	(1)	0
Estimated Fair Value	2,478	2,026
U.S. treasury securities
Available-for-Sale Debt Securities
Amortized Cost	464	308
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	0
Estimated Fair Value	464	309
Certificates of deposit
Available-for-Sale Debt Securities
Amortized Cost	358	216
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	358	216
Non-U.S. government securities
Available-for-Sale Debt Securities
Amortized Cost	62	43
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	62	43
Corporate debt securities
Available-for-Sale Debt Securities
Amortized Cost	1,247	1,140
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(1)	0
Estimated Fair Value	1,247	1,142
Residential mortgage and asset-backed securities
Available-for-Sale Debt Securities
Amortized Cost	347	316
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 347	$ 316

X

- Definition

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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