INVESTMENT SECURITIES - Schedule of Amortized Cost and Fair Value of Investment Securities (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Investment securities available for sale
Amortized Cost	$ 27,959	$ 20,688
Gross Unrealized Gains	37	115
Gross Unrealized Losses	(943)	(867)
Investment securities available for sale	27,053	19,936
Investment in marketable equity securities
Amortized Cost	75	75
Gross Unrealized Gains	13	17
Gross Unrealized Losses	(10)	(8)
Fair Value	78	84
Investment securities held to maturity
Amortized Cost	10,535	9,979
Gross Unrealized Gains	5	0
Gross Unrealized Losses	(1,594)	(1,476)
Fair Value	8,946	8,503
Total investment securities
Amortized Cost	38,569	30,742
Gross Unrealized Gains	55	132
Gross Unrealized Losses	(2,547)	(2,351)
Fair Value	36,077	28,523
U.S. Treasury
Investment securities available for sale
Amortized Cost	11,818	10,554
Gross Unrealized Gains	3	34
Gross Unrealized Losses	(70)	(80)
Investment securities available for sale	11,751	10,508
Investment securities held to maturity
Amortized Cost	481	479
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(41)	(40)
Fair Value	440	439
Government agency
Investment securities available for sale
Amortized Cost	99	120
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	(3)
Investment securities available for sale	97	117
Investment securities held to maturity
Amortized Cost	1,510	1,506
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(143)	(143)
Fair Value	1,367	1,363
Residential mortgage-backed securities
Investment securities available for sale
Amortized Cost	12,561	7,154
Gross Unrealized Gains	33	72
Gross Unrealized Losses	(619)	(540)
Investment securities available for sale	11,975	6,686
Investment securities held to maturity
Amortized Cost	4,793	4,205
Gross Unrealized Gains	5	0
Gross Unrealized Losses	(705)	(644)
Fair Value	4,093	3,561
Commercial mortgage-backed securities
Investment securities available for sale
Amortized Cost	2,938	2,319
Gross Unrealized Gains	1	9
Gross Unrealized Losses	(212)	(197)
Investment securities available for sale	2,727	2,131
Investment securities held to maturity
Amortized Cost	3,450	3,489
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(668)	(614)
Fair Value	2,782	2,875
Corporate bonds
Investment securities available for sale
Amortized Cost	526	529
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(40)	(47)
Investment securities available for sale	486	482
Municipal bonds
Investment securities available for sale
Amortized Cost	17	12
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available for sale	17	12
Supranational securities
Investment securities held to maturity
Amortized Cost	299	298
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(37)	(35)
Fair Value	262	263
Other
Investment securities held to maturity
Amortized Cost	2	2
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 2	$ 2

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