INVESTMENT SECURITIES - Gross Unrealized Losses and Fair Values of Securities (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Fair Value
Less than 12 months	$ 3,680	$ 4,419
12 months or more	9,082	8,962
Total	12,762	13,381
Gross Unrealized Losses
Less than 12 months	(98)	(270)
12 months or more	(1,381)	(1,431)
Total	(1,479)	(1,701)
U.S. Treasury and agency obligations
Fair Value
Less than 12 months	290	512
12 months or more	396	397
Total	686	909
Gross Unrealized Losses
Less than 12 months	(2)	(5)
12 months or more	(45)	(50)
Total	(47)	(55)
Mortgage-backed securities
Fair Value
Less than 12 months	867	1,231
12 months or more	2,123	1,683
Total	2,990	2,914
Gross Unrealized Losses
Less than 12 months	(17)	(104)
12 months or more	(406)	(367)
Total	(423)	(471)
Tax-exempt municipal securities
Fair Value
Less than 12 months	343	64
12 months or more	314	615
Total	657	679
Gross Unrealized Losses
Less than 12 months	(5)	(2)
12 months or more	(22)	(36)
Total	(27)	(38)
Residential
Fair Value
Less than 12 months	25	124
12 months or more	369	274
Total	394	398
Gross Unrealized Losses
Less than 12 months	(2)	(16)
12 months or more	(71)	(60)
Total	(73)	(76)
Commercial
Fair Value
Less than 12 months	119	243
12 months or more	1,275	1,157
Total	1,394	1,400
Gross Unrealized Losses
Less than 12 months	(4)	(13)
12 months or more	(145)	(142)
Total	(149)	(155)
Asset-backed securities
Fair Value
Less than 12 months	583	620
12 months or more	971	1,011
Total	1,554	1,631
Gross Unrealized Losses
Less than 12 months	(21)	(32)
12 months or more	(43)	(46)
Total	(64)	(78)
Corporate debt securities
Fair Value
Less than 12 months	1,453	1,625
12 months or more	3,634	3,825
Total	5,087	5,450
Gross Unrealized Losses
Less than 12 months	(47)	(98)
12 months or more	(649)	(730)
Total	$ (696)	$ (828)