INVESTMENT SECURITIES - Gross Unrealized Losses and Fair Values of Securities (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Fair Value
Less than 12 months	$ 4,989	$ 4,419
12 months or more	9,981	8,962
Total	14,970	13,381
Gross Unrealized Losses
Less than 12 months	(103)	(270)
12 months or more	(1,500)	(1,431)
Total	(1,603)	(1,701)
U.S. Treasury and agency obligations
Fair Value
Less than 12 months	1,334	512
12 months or more	408	397
Total	1,742	909
Gross Unrealized Losses
Less than 12 months	(17)	(5)
12 months or more	(48)	(50)
Total	(65)	(55)
Mortgage-backed securities
Fair Value
Less than 12 months	1,349	1,231
12 months or more	2,086	1,683
Total	3,435	2,914
Gross Unrealized Losses
Less than 12 months	(36)	(104)
12 months or more	(432)	(367)
Total	(468)	(471)
Tax-exempt municipal securities
Fair Value
Less than 12 months	337	64
12 months or more	373	615
Total	710	679
Gross Unrealized Losses
Less than 12 months	(5)	(2)
12 months or more	(26)	(36)
Total	(31)	(38)
Residential
Fair Value
Less than 12 months	17	124
12 months or more	374	274
Total	391	398
Gross Unrealized Losses
Less than 12 months	(1)	(16)
12 months or more	(74)	(60)
Total	(75)	(76)
Commercial
Fair Value
Less than 12 months	26	243
12 months or more	1,365	1,157
Total	1,391	1,400
Gross Unrealized Losses
Less than 12 months	(1)	(13)
12 months or more	(159)	(142)
Total	(160)	(155)
Asset-backed securities
Fair Value
Less than 12 months	535	620
12 months or more	1,263	1,011
Total	1,798	1,631
Gross Unrealized Losses
Less than 12 months	(12)	(32)
12 months or more	(55)	(46)
Total	(67)	(78)
Corporate debt securities
Fair Value
Less than 12 months	1,391	1,625
12 months or more	4,112	3,825
Total	5,503	5,450
Gross Unrealized Losses
Less than 12 months	(31)	(98)
12 months or more	(706)	(730)
Total	$ (737)	$ (828)