INVESTMENT SECURITIES - Gross Unrealized Losses and Fair Values of Securities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fair Value
Less than 12 months	$ 3,621	$ 4,419
12 months or more	11,046	8,962
Total	14,667	13,381
Gross Unrealized Losses
Less than 12 months	(28)	(270)
12 months or more	(1,300)	(1,431)
Total	(1,328)	(1,701)
U.S. Treasury and agency obligations
Fair Value
Less than 12 months	1,899	512
12 months or more	431	397
Total	2,330	909
Gross Unrealized Losses
Less than 12 months	(12)	(5)
12 months or more	(39)	(50)
Total	(51)	(55)
Mortgage-backed securities
Fair Value
Less than 12 months	958	1,231
12 months or more	2,269	1,683
Total	3,227	2,914
Gross Unrealized Losses
Less than 12 months	(12)	(104)
12 months or more	(413)	(367)
Total	(425)	(471)
Tax-exempt municipal securities
Fair Value
Less than 12 months	160	64
12 months or more	523	615
Total	683	679
Gross Unrealized Losses
Less than 12 months	(1)	(2)
12 months or more	(21)	(36)
Total	(22)	(38)
Residential
Fair Value
Less than 12 months	0	124
12 months or more	373	274
Total	373	398
Gross Unrealized Losses
Less than 12 months	0	(16)
12 months or more	(66)	(60)
Total	(66)	(76)
Commercial
Fair Value
Less than 12 months	18	243
12 months or more	1,303	1,157
Total	1,321	1,400
Gross Unrealized Losses
Less than 12 months	0	(13)
12 months or more	(126)	(142)
Total	(126)	(155)
Asset-backed securities
Fair Value
Less than 12 months	120	620
12 months or more	1,364	1,011
Total	1,484	1,631
Gross Unrealized Losses
Less than 12 months	(1)	(32)
12 months or more	(43)	(46)
Total	(44)	(78)
Corporate debt securities
Fair Value
Less than 12 months	466	1,625
12 months or more	4,783	3,825
Total	5,249	5,450
Gross Unrealized Losses
Less than 12 months	(2)	(98)
12 months or more	(592)	(730)
Total	$ (594)	$ (828)