INVESTMENT SECURITIES - Securities Classified as Current and Long-Term (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	$ 13,925	$ 12,437
Gross Unrealized Gains	301	520
Gross Unrealized Losses	(113)	(6)
Fair Value	14,113	12,951
Common stock	701	815
Total investment securities	14,814	13,766
U.S. Treasury and agency obligations
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	656	616
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(7)	(1)
Fair Value	650	616
Mortgage-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	3,699	3,115
Gross Unrealized Gains	69	140
Gross Unrealized Losses	(46)	(1)
Fair Value	3,722	3,254
Tax-exempt municipal securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	853	1,393
Gross Unrealized Gains	35	54
Gross Unrealized Losses	(2)	0
Fair Value	886	1,447
Residential
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	392	17
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3)	0
Fair Value	389	17
Commercial
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1,438	1,260
Gross Unrealized Gains	37	59
Gross Unrealized Losses	(7)	(1)
Fair Value	1,468	1,318
Asset-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1,394	1,364
Gross Unrealized Gains	7	10
Gross Unrealized Losses	(1)	(2)
Fair Value	1,400	1,372
Corporate debt securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	5,493	4,672
Gross Unrealized Gains	152	256
Gross Unrealized Losses	(47)	(1)
Fair Value	$ 5,598	$ 4,927

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), classified as current.

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