INVESTMENT SECURITIES AND OTHER SECURITIES - Continuous Unrealized Loss Position (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Available-for-sale securities:
Less than 12 Months, Fair Value	$ 11,073	$ 1,198
Less than 12 Months, Gross Unrealized Losses	(53)	(14)
Over 12 Months, Fair Value	15,900	16,499
Over 12 Months, Gross Unrealized Losses	(2,469)	(2,430)
Total, Fair Value	26,973	17,697
Total, Gross Unrealized Losses	(2,522)	(2,444)
Held-to-maturity securities:
Less than 12 Months, Fair Value	885	48
Less than 12 Months, Gross Unrealized Losses	(5)	0
Over 12 Months, Fair Value	10,444	11,079
Over 12 Months, Gross Unrealized Losses	(1,683)	(1,647)
Total held-to-maturity securities	11,329	11,127
Total, Gross Unrealized Losses	(1,688)	(1,647)
U.S. Treasury
Available-for-sale securities:
Less than 12 Months, Fair Value	3,883	0
Less than 12 Months, Gross Unrealized Losses	(7)	0
Over 12 Months, Fair Value	0	439
Over 12 Months, Gross Unrealized Losses	0	0
Total, Fair Value	3,883	439
Total, Gross Unrealized Losses	(7)	0
Held-to-maturity securities:
Less than 12 Months, Fair Value	747	0
Less than 12 Months, Gross Unrealized Losses	(3)	0
Over 12 Months, Fair Value	0	289
Over 12 Months, Gross Unrealized Losses	0	0
Total held-to-maturity securities	747	289
Total, Gross Unrealized Losses	(3)	0
Total U.S. Treasury, federal agency, and other agency securities
Available-for-sale securities:
Less than 12 Months, Fair Value	9,710	144
Less than 12 Months, Gross Unrealized Losses	(37)	0
Over 12 Months, Fair Value	13,197	14,145
Over 12 Months, Gross Unrealized Losses	(2,352)	(2,333)
Total, Fair Value	22,907	14,289
Total, Gross Unrealized Losses	(2,389)	(2,333)
Held-to-maturity securities:
Less than 12 Months, Fair Value	885	48
Less than 12 Months, Gross Unrealized Losses	(5)	0
Over 12 Months, Fair Value	10,443	11,078
Over 12 Months, Gross Unrealized Losses	(1,683)	(1,647)
Total held-to-maturity securities	11,328	11,126
Total, Gross Unrealized Losses	(1,688)	(1,647)
Residential MBS
Available-for-sale securities:
Less than 12 Months, Fair Value	3,290	55
Less than 12 Months, Gross Unrealized Losses	(20)	0
Over 12 Months, Fair Value	8,946	9,185
Over 12 Months, Gross Unrealized Losses	(1,363)	(1,365)
Total, Fair Value	12,236	9,240
Total, Gross Unrealized Losses	(1,383)	(1,365)
Held-to-maturity securities:
Less than 12 Months, Fair Value	67	0
Less than 12 Months, Gross Unrealized Losses	(1)	0
Over 12 Months, Fair Value	6,489	6,694
Over 12 Months, Gross Unrealized Losses	(946)	(941)
Total held-to-maturity securities	6,556	6,694
Total, Gross Unrealized Losses	(947)	(941)
Residential CMO
Available-for-sale securities:
Less than 12 Months, Fair Value	1,606	51
Less than 12 Months, Gross Unrealized Losses	(6)	0
Over 12 Months, Fair Value	2,406	2,665
Over 12 Months, Gross Unrealized Losses	(331)	(308)
Total, Fair Value	4,012	2,716
Total, Gross Unrealized Losses	(337)	(308)
Held-to-maturity securities:
Less than 12 Months, Fair Value	71	48
Less than 12 Months, Gross Unrealized Losses	(1)	0
Over 12 Months, Fair Value	2,852	2,956
Over 12 Months, Gross Unrealized Losses	(548)	(520)
Total held-to-maturity securities	2,923	3,004
Total, Gross Unrealized Losses	(549)	(520)
Commercial MBS
Available-for-sale securities:
Less than 12 Months, Fair Value	870	23
Less than 12 Months, Gross Unrealized Losses	(4)	0
Over 12 Months, Fair Value	1,776	1,782
Over 12 Months, Gross Unrealized Losses	(656)	(657)
Total, Fair Value	2,646	1,805
Total, Gross Unrealized Losses	(660)	(657)
Held-to-maturity securities:
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Gross Unrealized Losses	0	0
Over 12 Months, Fair Value	1,062	1,094
Over 12 Months, Gross Unrealized Losses	(187)	(184)
Total held-to-maturity securities	1,062	1,094
Total, Gross Unrealized Losses	(187)	(184)
Other agencies
Available-for-sale securities:
Less than 12 Months, Fair Value	61	15
Less than 12 Months, Gross Unrealized Losses	0	0
Over 12 Months, Fair Value	69	74
Over 12 Months, Gross Unrealized Losses	(2)	(3)
Total, Fair Value	130	89
Total, Gross Unrealized Losses	(2)	(3)
Held-to-maturity securities:
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Gross Unrealized Losses	0	0
Over 12 Months, Fair Value	40	45
Over 12 Months, Gross Unrealized Losses	(2)	(2)
Total held-to-maturity securities	40	45
Total, Gross Unrealized Losses	(2)	(2)
Municipal securities
Available-for-sale securities:
Less than 12 Months, Fair Value	1,358	1,043
Less than 12 Months, Gross Unrealized Losses	(16)	(14)
Over 12 Months, Fair Value	2,307	1,892
Over 12 Months, Gross Unrealized Losses	(86)	(67)
Total, Fair Value	3,665	2,935
Total, Gross Unrealized Losses	(102)	(81)
Held-to-maturity securities:
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Gross Unrealized Losses	0	0
Over 12 Months, Fair Value	1	1
Over 12 Months, Gross Unrealized Losses	0	0
Total held-to-maturity securities	1	1
Total, Gross Unrealized Losses	0	0
Corporate debt
Available-for-sale securities:
Less than 12 Months, Fair Value	2	2
Less than 12 Months, Gross Unrealized Losses	0	0
Over 12 Months, Fair Value	174	176
Over 12 Months, Gross Unrealized Losses	(17)	(15)
Total, Fair Value	176	178
Total, Gross Unrealized Losses	(17)	(15)
Asset-backed securities
Available-for-sale securities:
Less than 12 Months, Fair Value	0	9
Less than 12 Months, Gross Unrealized Losses	0	0
Over 12 Months, Fair Value	149	207
Over 12 Months, Gross Unrealized Losses	(7)	(8)
Total, Fair Value	149	216
Total, Gross Unrealized Losses	(7)	(8)
Private-label CMO
Available-for-sale securities:
Less than 12 Months, Fair Value	3	0
Less than 12 Months, Gross Unrealized Losses	0	0
Over 12 Months, Fair Value	73	79
Over 12 Months, Gross Unrealized Losses	(7)	(7)
Total, Fair Value	76	79
Total, Gross Unrealized Losses	$ (7)	$ (7)

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