INVESTMENT SECURITIES - Classified as Current and Long-Term (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities Amortized Cost to Fair Value
Amortized Cost	$ 12,437	$ 11,160
Gross Unrealized Gains	520	219
Gross Unrealized Losses	(6)	(8)
Fair Value	12,951	11,371
Common stock	815	7
Total investment securities	13,766	11,378
U.S. Treasury and agency obligations
Debt Securities Amortized Cost to Fair Value
Amortized Cost	616	353
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(1)	0
Fair Value	616	354
Mortgage-backed securities
Debt Securities Amortized Cost to Fair Value
Amortized Cost	3,115	3,628
Gross Unrealized Gains	140	85
Gross Unrealized Losses	(1)	(3)
Fair Value	3,254	3,710
Tax-exempt municipal securities
Debt Securities Amortized Cost to Fair Value
Amortized Cost	1,393	1,433
Gross Unrealized Gains	54	30
Gross Unrealized Losses	0	0
Fair Value	1,447	1,463
Residential mortgage-backed securities
Debt Securities Amortized Cost to Fair Value
Amortized Cost	17
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	17
Commercial mortgage-backed securities
Debt Securities Amortized Cost to Fair Value
Amortized Cost	1,260	786
Gross Unrealized Gains	59	18
Gross Unrealized Losses	(1)	0
Fair Value	1,318	804
Asset-backed securities
Debt Securities Amortized Cost to Fair Value
Amortized Cost	1,364	1,093
Gross Unrealized Gains	10	3
Gross Unrealized Losses	(2)	(3)
Fair Value	1,372	1,093
Corporate debt securities
Debt Securities Amortized Cost to Fair Value
Amortized Cost	4,672	3,867
Gross Unrealized Gains	256	82
Gross Unrealized Losses	(1)	(2)
Fair Value	$ 4,927	$ 3,947

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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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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