INVESTMENT SECURITIES - Securities Classified as Current and Long-Term (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	$ 12,799	$ 11,160
Gross Unrealized Gains	459	219
Gross Unrealized Losses	(33)	(8)
Fair Value	13,225	11,371
U.S. Treasury and agency obligations
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	929	353
Gross Unrealized Gains	3	1
Gross Unrealized Losses	0	0
Fair Value	932	354
Mortgage-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	3,861	3,628
Gross Unrealized Gains	183	85
Gross Unrealized Losses	(1)	(3)
Fair Value	4,043	3,710
Tax-exempt municipal securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1,464	1,433
Gross Unrealized Gains	35	30
Gross Unrealized Losses	(3)	0
Fair Value	1,496	1,463
Commercial mortgage-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	961	786
Gross Unrealized Gains	44	18
Gross Unrealized Losses	(4)	0
Fair Value	1,001	804
Asset-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1,186	1,093
Gross Unrealized Gains	4	3
Gross Unrealized Losses	(17)	(3)
Fair Value	1,173	1,093
Corporate debt securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	4,398	3,867
Gross Unrealized Gains	190	82
Gross Unrealized Losses	(8)	(2)
Fair Value	$ 4,580	$ 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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