INVESTMENT SECURITIES - Securities Classified as Current and Long-Term (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	$ 10,561	$ 10,641
Gross Unrealized Gains	253	9
Gross Unrealized Losses	(10)	(213)
Fair Value	10,804	10,437
Investment in equity securities	30
U.S. Treasury and agency obligations
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	373	419
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(1)	(3)
Fair Value	374	417
Mortgage-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	3,543	2,595
Gross Unrealized Gains	101	3
Gross Unrealized Losses	(3)	(54)
Fair Value	3,641	2,544
Tax-exempt municipal securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1,465	2,805
Gross Unrealized Gains	36	3
Gross Unrealized Losses	0	(37)
Fair Value	1,501	2,771
Residential mortgage-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	0	55
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	55
Commercial mortgage-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	641	537
Gross Unrealized Gains	27	0
Gross Unrealized Losses	0	(14)
Fair Value	668	523
Asset-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1,030	991
Gross Unrealized Gains	3	1
Gross Unrealized Losses	(3)	(7)
Fair Value	1,030	985
Corporate debt securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	3,509	3,239
Gross Unrealized Gains	84	1
Gross Unrealized Losses	(3)	(98)
Fair Value	$ 3,590	$ 3,142

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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