INVESTMENT SECURITIES - Schedule of Amortized Cost and Fair Value of Investment Securities (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Investment securities available for sale
Amortized Cost	$ 35,187	$ 34,512
Gross Unrealized Gains	317	81
Gross Unrealized Losses	(541)	(843)
Investment securities available for sale	34,963	33,750
Investment in marketable equity securities
Amortized Cost	78	79
Gross Unrealized Gains	33	27
Gross Unrealized Losses	(1)	(5)
Fair Value	110	101
Investment securities held to maturity
Amortized Cost	10,051	10,239
Gross Unrealized Gains	28	2
Gross Unrealized Losses	(1,241)	(1,539)
Fair Value	8,838	8,702
Total investment securities
Amortized Cost	45,316	44,830
Gross Unrealized Gains	378	110
Gross Unrealized Losses	(1,783)	(2,387)
Fair Value	43,911	42,553
U.S. Treasury
Investment securities available for sale
Amortized Cost	13,729	13,897
Gross Unrealized Gains	54	33
Gross Unrealized Losses	(2)	(27)
Investment securities available for sale	13,781	13,903
Investment securities held to maturity
Amortized Cost	387	483
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(18)	(31)
Fair Value	369	452
Government agency
Investment securities available for sale
Amortized Cost	53	79
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(2)
Investment securities available for sale	52	77
Investment securities held to maturity
Amortized Cost	1,459	1,489
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(64)	(115)
Fair Value	1,395	1,374
Residential mortgage-backed securities
Investment securities available for sale
Amortized Cost	17,550	16,161
Gross Unrealized Gains	236	41
Gross Unrealized Losses	(351)	(582)
Investment securities available for sale	17,435	15,620
Investment securities held to maturity
Amortized Cost	4,568	4,558
Gross Unrealized Gains	28	2
Gross Unrealized Losses	(513)	(682)
Fair Value	4,083	3,878
Commercial mortgage-backed securities
Investment securities available for sale
Amortized Cost	3,582	3,869
Gross Unrealized Gains	27	7
Gross Unrealized Losses	(181)	(210)
Investment securities available for sale	3,428	3,666
Investment securities held to maturity
Amortized Cost	3,358	3,407
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(625)	(678)
Fair Value	2,733	2,729
Corporate bonds
Investment securities available for sale
Amortized Cost	256	489
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6)	(22)
Investment securities available for sale	250	467
Municipal bonds
Investment securities available for sale
Amortized Cost	17	17
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available for sale	17	17
Supranational securities
Investment securities held to maturity
Amortized Cost	277	300
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(21)	(33)
Fair Value	256	267
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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