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INVESTMENT SECURITIES (Summary of Amount of Gross Unrealized Losses for Debt Securities and Estimated Fair Value) (Details) - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
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Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-sale, less than 12 Months | $ 0 | $ 3
Available-for-sale, 12 Months or more | 1,228 | 1,504
Available-for-sale, total | 1,228 | 1,507
Available-for-sale, less than 12 Months, estimated fair value | 131 | 390
Available-for-sale, 12 months or more, estimated fair value | 7,596 | 8,230
Available-for-sale, total, estimated fair value | 7,727 | 8,620
U.S. Treasury securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-sale, less than 12 Months | 0 | 3
Available-for-sale, 12 Months or more | 105 | 116
Available-for-sale, total | 105 | 119
Available-for-sale, less than 12 Months, estimated fair value | 0 | 198
Available-for-sale, 12 months or more, estimated fair value | 296 | 285
Available-for-sale, total, estimated fair value | 296 | 483
Agency securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-sale, less than 12 Months | 0 | 0
Available-for-sale, 12 Months or more | 17 | 26
Available-for-sale, total | 17 | 26
Available-for-sale, less than 12 Months, estimated fair value | 7 | 3
Available-for-sale, 12 months or more, estimated fair value | 320 | 403
Available-for-sale, total, estimated fair value | 327 | 406
Agency guaranteed mortgage-backed securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-sale, less than 12 Months | 0 | 0
Available-for-sale, 12 Months or more | 1,041 | 1,263
Available-for-sale, total | 1,041 | 1,263
Available-for-sale, less than 12 Months, estimated fair value | 6 | 86
Available-for-sale, 12 months or more, estimated fair value | 5,846 | 6,171
Available-for-sale, total, estimated fair value | 5,852 | 6,257
Small Business Administration loan-backed securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-sale, less than 12 Months | 0 | 0
Available-for-sale, 12 Months or more | 16 | 21
Available-for-sale, total | 16 | 21
Available-for-sale, less than 12 Months, estimated fair value | 32 | 35
Available-for-sale, 12 months or more, estimated fair value | 321 | 387
Available-for-sale, total, estimated fair value | 353 | 422
Municipal securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-sale, less than 12 Months | 0 | 0
Available-for-sale, 12 Months or more | 49 | 78
Available-for-sale, total | 49 | 78
Available-for-sale, less than 12 Months, estimated fair value | 86 | 68
Available-for-sale, 12 months or more, estimated fair value | 813 | 984
Available-for-sale, total, estimated fair value | $ 899 | $ 1,052

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