INVESTMENT SECURITIES - Gross Unrealized Losses and Fair Values of Securities (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Fair Value
Less than 12 months	$ 1,549	$ 3,621
12 months or more	9,835	11,046
Total	11,384	14,667
Gross Unrealized Losses
Less than 12 months	(9)	(28)
12 months or more	(989)	(1,300)
Total	(998)	(1,328)
U.S. Treasury and agency obligations
Fair Value
Less than 12 months	551	1,899
12 months or more	518	431
Total	1,069	2,330
Gross Unrealized Losses
Less than 12 months	(2)	(12)
12 months or more	(31)	(39)
Total	(33)	(51)
Mortgage-backed securities
Fair Value
Less than 12 months	330	958
12 months or more	2,378	2,269
Total	2,708	3,227
Gross Unrealized Losses
Less than 12 months	(2)	(12)
12 months or more	(349)	(413)
Total	(351)	(425)
Tax-exempt municipal securities
Fair Value
Less than 12 months	77	160
12 months or more	417	523
Total	494	683
Gross Unrealized Losses
Less than 12 months	0	(1)
12 months or more	(18)	(21)
Total	(18)	(22)
Residential
Fair Value
Less than 12 months	57	0
12 months or more	361	373
Total	418	373
Gross Unrealized Losses
Less than 12 months	(2)	0
12 months or more	(52)	(66)
Total	(54)	(66)
Commercial
Fair Value
Less than 12 months	26	18
12 months or more	1,124	1,303
Total	1,150	1,321
Gross Unrealized Losses
Less than 12 months	(1)	0
12 months or more	(77)	(126)
Total	(78)	(126)
Asset-backed securities
Fair Value
Less than 12 months	218	120
12 months or more	571	1,364
Total	789	1,484
Gross Unrealized Losses
Less than 12 months	(1)	(1)
12 months or more	(19)	(43)
Total	(20)	(44)
Corporate debt securities
Fair Value
Less than 12 months	290	466
12 months or more	4,466	4,783
Total	4,756	5,249
Gross Unrealized Losses
Less than 12 months	(1)	(2)
12 months or more	(443)	(592)
Total	$ (444)	$ (594)