INVESTMENT SECURITIES - Schedule of Amortized Cost and Fair Value of Investment Securities (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Investment securities available for sale
Amortized Cost	$ 25,791	$ 20,688
Gross Unrealized Gains	51	115
Gross Unrealized Losses	(927)	(867)
Investment securities available for sale	24,915	19,936
Investment in marketable equity securities
Amortized Cost	75	75
Gross Unrealized Gains	13	17
Gross Unrealized Losses	(9)	(8)
Fair Value	79	84
Investment securities held to maturity
Amortized Cost	10,050	9,979
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,571)	(1,476)
Fair Value	8,479	8,503
Total investment securities
Amortized Cost	35,916	30,742
Gross Unrealized Gains	64	132
Gross Unrealized Losses	(2,507)	(2,351)
Fair Value	33,473	28,523
U.S. Treasury
Investment securities available for sale
Amortized Cost	11,907	10,554
Gross Unrealized Gains	7	34
Gross Unrealized Losses	(78)	(80)
Investment securities available for sale	11,836	10,508
Investment securities held to maturity
Amortized Cost	480	479
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(42)	(40)
Fair Value	438	439
Government agency
Investment securities available for sale
Amortized Cost	110	120
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3)	(3)
Investment securities available for sale	107	117
Investment securities held to maturity
Amortized Cost	1,508	1,506
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(150)	(143)
Fair Value	1,358	1,363
Residential mortgage-backed securities
Investment securities available for sale
Amortized Cost	10,665	7,154
Gross Unrealized Gains	42	72
Gross Unrealized Losses	(597)	(540)
Investment securities available for sale	10,110	6,686
Investment securities held to maturity
Amortized Cost	4,293	4,205
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(697)	(644)
Fair Value	3,596	3,561
Commercial mortgage-backed securities
Investment securities available for sale
Amortized Cost	2,566	2,319
Gross Unrealized Gains	2	9
Gross Unrealized Losses	(207)	(197)
Investment securities available for sale	2,361	2,131
Investment securities held to maturity
Amortized Cost	3,469	3,489
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(645)	(614)
Fair Value	2,824	2,875
Corporate bonds
Investment securities available for sale
Amortized Cost	529	529
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(42)	(47)
Investment securities available for sale	487	482
Municipal bonds
Investment securities available for sale
Amortized Cost	14	12
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available for sale	14	12
Supranational securities
Investment securities held to maturity
Amortized Cost	298	298
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(37)	(35)
Fair Value	261	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

Equity Securities FV-NI, Accumulated Gross Unrealized Gain, before Tax

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