INVESTMENT SECURITIES - Gross Unrealized Losses and Fair Values of Securities (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Fair Value
Less than 12 months	$ 4,212	$ 4,419
12 months or more	10,836	8,962
Total	15,048	13,381
Gross Unrealized Losses
Less than 12 months	(165)	(270)
12 months or more	(1,800)	(1,431)
Total	(1,965)	(1,701)
U.S. Treasury and agency obligations
Fair Value
Less than 12 months	1,483	512
12 months or more	407	397
Total	1,890	909
Gross Unrealized Losses
Less than 12 months	(51)	(5)
12 months or more	(54)	(50)
Total	(105)	(55)
Mortgage-backed securities
Fair Value
Less than 12 months	1,084	1,231
12 months or more	2,169	1,683
Total	3,253	2,914
Gross Unrealized Losses
Less than 12 months	(66)	(104)
12 months or more	(571)	(367)
Total	(637)	(471)
Tax-exempt municipal securities
Fair Value
Less than 12 months	278	64
12 months or more	515	615
Total	793	679
Gross Unrealized Losses
Less than 12 months	(6)	(2)
12 months or more	(44)	(36)
Total	(50)	(38)
Residential
Fair Value
Less than 12 months	48	124
12 months or more	363	274
Total	411	398
Gross Unrealized Losses
Less than 12 months	(1)	(16)
12 months or more	(84)	(60)
Total	(85)	(76)
Commercial
Fair Value
Less than 12 months	15	243
12 months or more	1,304	1,157
Total	1,319	1,400
Gross Unrealized Losses
Less than 12 months	0	(13)
12 months or more	(155)	(142)
Total	(155)	(155)
Asset-backed securities
Fair Value
Less than 12 months	343	620
12 months or more	1,430	1,011
Total	1,773	1,631
Gross Unrealized Losses
Less than 12 months	(6)	(32)
12 months or more	(59)	(46)
Total	(65)	(78)
Corporate debt securities
Fair Value
Less than 12 months	961	1,625
12 months or more	4,648	3,825
Total	5,609	5,450
Gross Unrealized Losses
Less than 12 months	(35)	(98)
12 months or more	(833)	(730)
Total	$ (868)	$ (828)