INVESTMENT SECURITIES - Securities Classified as Current and Long-Term (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	$ 12,642	$ 11,160
Gross Unrealized Gains	505	219
Gross Unrealized Losses	(14)	(8)
Fair Value	13,133	11,371
Common stock	713	7
Total investment securities	13,846	11,378
U.S. Treasury and agency obligations
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1,195	353
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(1)	0
Fair Value	1,196	354
Mortgage-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	3,511	3,628
Gross Unrealized Gains	183	85
Gross Unrealized Losses	(2)	(3)
Fair Value	3,692	3,710
Tax-exempt municipal securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1,439	1,433
Gross Unrealized Gains	40	30
Gross Unrealized Losses	(3)	0
Fair Value	1,476	1,463
Commercial mortgage-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1,020	786
Gross Unrealized Gains	54	18
Gross Unrealized Losses	(1)	0
Fair Value	1,073	804
Asset-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1,278	1,093
Gross Unrealized Gains	8	3
Gross Unrealized Losses	(5)	(3)
Fair Value	1,281	1,093
Corporate debt securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	4,199	3,867
Gross Unrealized Gains	218	82
Gross Unrealized Losses	(2)	(2)
Fair Value	$ 4,415	$ 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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