INVESTMENT SECURITIES - Securities Classified as Current and Long-Term (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	$ 10,245	$ 10,641
Gross Unrealized Gains	174	9
Gross Unrealized Losses	(17)	(213)
Fair Value	10,402	10,437
U.S. Treasury and agency obligations
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	370	419
Gross Unrealized Gains	2	1
Gross Unrealized Losses	0	(3)
Fair Value	372	417
Mortgage-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	3,459	2,595
Gross Unrealized Gains	69	3
Gross Unrealized Losses	(8)	(54)
Fair Value	3,520	2,544
Tax-exempt municipal securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1,632	2,805
Gross Unrealized Gains	28	3
Gross Unrealized Losses	(1)	(37)
Fair Value	1,659	2,771
Residential mortgage-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1	55
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	1	55
Commercial mortgage-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	621	537
Gross Unrealized Gains	17	0
Gross Unrealized Losses	0	(14)
Fair Value	638	523
Asset-backed securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	1,037	991
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(3)	(7)
Fair Value	1,036	985
Corporate debt securities
Investment Securities, Available-for-sale Amortized Cost to Fair Value
Amortized Cost	3,125	3,239
Gross Unrealized Gains	56	1
Gross Unrealized Losses	(5)	(98)
Fair Value	$ 3,176	$ 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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