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Loans Held-for-Investment and Allowance for Credit Losses - Schedule of Company's Internal Ratings of its Loans Held-for-Investment, Including The Year of Origination, by Portfolio Segments (Detail) - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024 | Sep. 30, 2024
--- | --- | --- | ---
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | $ 2,552 |  |
2024 | 1,749 | $ 3,112 | $ 2,397
2023 | 910 | 1,205 | 1,478
2022 | 1,317 | 1,571 | 1,671
2021 | 710 | 836 | 905
2020 |  | 355 | 405
Prior | 768 | 637 | 689
Revolving Loans Amortized Cost Basis | 238 | 198 | 179
Total | 8,244 | 7,914 | 7,724
Charge-Off [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2023 | 23 | 3 | 1
2022 | 1 | 2 | 2
Prior |  |  | 0
Total | 24 | 5 | 3
C&I [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 526 |  |
2024 | 330 | 696 | 547
2023 | 139 | 229 | 335
2022 | 105 | 151 | 178
2021 | 37 | 46 | 58
2020 |  | 24 | 26
Prior | 38 | 31 | 32
Revolving Loans Amortized Cost Basis | 0 | 0 | 0
Total | 1,175 | 1,177 | 1,176
C&I [Member] | Charge-Off [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2023 | 17 | 1 | 1
Total | 17 | 1 | 1
Municipal [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 124 |  |
2024 | 50 | 175 | 131
2023 | 24 | 26 | 29
2022 | 72 | 77 | 79
2021 | 11 | 12 | 13
2020 |  | 8 | 9
Prior | 67 | 71 | 73
Revolving Loans Amortized Cost Basis | 0 | 0 | 0
Total | 348 | 369 | 334
Agriculture [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 63 |  |
2024 | 18 | 79 | 56
2023 | 3 | 8 | 19
2022 | 4 | 5 | 5
2021 | 1 | 2 | 2
2020 |  | 1 | 1
Prior | 0 | 0 | 0
Revolving Loans Amortized Cost Basis | 0 | 0 | 0
Total | 89 | 95 | 83
Construction & Development [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 648 |  |
2024 | 333 | 675 | 520
2023 | 100 | 134 | 229
2022 | 72 | 167 | 181
2021 | 47 | 56 | 57
2020 |  | 14 | 17
Prior | 14 | 8 | 9
Revolving Loans Amortized Cost Basis | 1 | 1 | 1
Total | 1,215 | 1,055 | 1,014
Farm [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 71 |  |
2024 | 61 | 115 | 76
2023 | 36 | 43 | 45
2022 | 62 | 76 | 80
2021 | 56 | 60 | 65
2020 |  | 22 | 24
Prior | 37 | 24 | 26
Revolving Loans Amortized Cost Basis | 0 |  | 0
Total | 323 | 340 | 316
Non-Owner Occupied CRE [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 145 |  |
2024 | 104 | 180 | 151
2023 | 66 | 90 | 94
2022 | 256 | 246 | 245
2021 | 127 | 140 | 163
2020 |  | 65 | 66
Prior | 104 | 85 | 107
Revolving Loans Amortized Cost Basis | 0 | 0 | 0
Total | 802 | 806 | 826
Non-Owner Occupied CRE [Member] | Charge-Off [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2023 | 1 | 1 |
Total | 1 | 1 |
Owner Occupied CRE [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 183 |  |
2024 | 149 | 173 | 132
2023 | 121 | 142 | 147
2022 | 284 | 305 | 321
2021 | 175 | 194 | 203
2020 |  | 100 | 106
Prior | 207 | 169 | 178
Revolving Loans Amortized Cost Basis | 0 | 0 | 0
Total | 1,119 | 1,083 | 1,087
Owner Occupied CRE [Member] | Charge-Off [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2023 | 4 |  |
Total | 4 |  |
Residential [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 438 |  |
2024 | 423 | 612 | 454
2023 | 322 | 375 | 400
2022 | 368 | 391 | 405
2021 | 231 | 273 | 283
2020 |  | 109 | 140
Prior | 297 | 246 | 259
Revolving Loans Amortized Cost Basis | 230 | 190 | 171
Total | 2,309 | 2,196 | 2,112
Residential [Member] | Charge-Off [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2023 | 1 |  |
Total | 1 |  |
Auto [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 298 |  |
2024 | 243 | 339 | 271
2023 | 79 | 123 | 138
2022 | 76 | 127 | 145
2021 | 19 | 39 | 46
2020 |  | 10 | 14
Prior | 3 | 2 | 4
Revolving Loans Amortized Cost Basis | 0 | 0 | 0
Total | 718 | 640 | 618
Auto [Member] | Charge-Off [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2023 |  | 1 |
2022 | 1 | 1 | 1
Total | 1 | 2 | 1
Non-Auto [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 56 |  |
2024 | 38 | 68 | 59
2023 | 20 | 35 | 42
2022 | 18 | 26 | 32
2021 | 6 | 14 | 15
2020 |  | 2 | 2
Prior | 1 | 1 | 1
Revolving Loans Amortized Cost Basis | 7 | 7 | 7
Total | 146 | 153 | 158
Non-Auto [Member] | Charge-Off [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2022 |  | 1 | 1
Total |  | 1 | 1
Pass [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 2,520 |  |
2024 | 1,713 | 3,057 | 2,359
2023 | 882 | 1,173 | 1,450
2022 | 1,254 | 1,506 | 1,605
2021 | 662 | 802 | 872
2020 |  | 338 | 388
Prior | 725 | 608 | 645
Revolving Loans Amortized Cost Basis | 235 | 196 | 175
Total | 7,991 | 7,680 | 7,494
Pass [Member] | C&I [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 514 |  |
2024 | 324 | 677 | 533
2023 | 136 | 226 | 331
2022 | 102 | 146 | 175
2021 | 22 | 45 | 57
2020 |  | 23 | 25
Prior | 37 | 30 | 30
Total | 1,135 | 1,147 | 1,151
Pass [Member] | Municipal [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 124 |  |
2024 | 50 | 175 | 131
2023 | 24 | 26 | 29
2022 | 71 | 77 | 79
2021 |  | 12 | 13
2020 |  | 8 | 9
Prior | 59 | 71 | 73
Total | 339 | 369 | 334
Pass [Member] | Agriculture [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 62 |  |
2024 | 17 | 76 | 53
2023 | 3 | 8 | 19
2022 | 3 | 4 | 5
2021 |  | 2 | 2
2020 |  | 1 | 1
Total | 86 | 91 | 80
Pass [Member] | Construction & Development [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 641 |  |
2024 | 327 | 667 | 513
2023 | 99 | 133 | 227
2022 | 71 | 166 | 180
2021 | 46 | 55 | 57
2020 |  | 14 | 17
Prior | 14 | 8 | 9
Revolving Loans Amortized Cost Basis | 1 | 1 | 1
Total | 1,199 | 1,044 | 1,004
Pass [Member] | Farm [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 70 |  |
2024 | 61 | 114 | 76
2023 | 36 | 42 | 44
2022 | 58 | 72 | 76
2021 | 55 | 60 | 65
2020 |  | 18 | 20
Prior | 33 | 23 | 25
Total | 313 | 329 | 306
Pass [Member] | Non-Owner Occupied CRE [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 138 |  |
2024 | 104 | 166 | 147
2023 | 61 | 86 | 91
2022 | 248 | 242 | 244
2021 | 115 | 133 | 155
2020 |  | 58 | 60
Prior | 99 | 81 | 91
Total | 765 | 766 | 788
Pass [Member] | Owner Occupied CRE [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 182 |  |
2024 | 140 | 170 | 128
2023 | 112 | 128 | 138
2022 | 254 | 270 | 279
2021 | 161 | 177 | 185
2020 |  | 99 | 104
Prior | 198 | 160 | 166
Total | 1,047 | 1,004 | 1,000
Pass [Member] | Residential [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 435 |  |
2024 | 410 | 606 | 448
2023 | 313 | 367 | 392
2022 | 355 | 378 | 392
2021 | 226 | 266 | 278
2020 |  | 105 | 136
Prior | 281 | 232 | 246
Revolving Loans Amortized Cost Basis | 227 | 188 | 167
Total | 2,247 | 2,142 | 2,059
Pass [Member] | Auto [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 298 |  |
2024 | 242 | 338 | 271
2023 | 78 | 122 | 137
2022 | 75 | 126 | 144
2021 | 19 | 38 | 45
2020 |  | 10 | 14
Prior | 3 | 2 | 4
Revolving Loans Amortized Cost Basis | 0 |  |
Total | 715 | 636 | 615
Pass [Member] | Non-Auto [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 56 |  |
2024 | 38 | 68 | 59
2023 | 20 | 35 | 42
2022 | 17 | 25 | 31
2021 | 6 | 14 | 15
2020 |  | 2 | 2
Prior | 1 | 1 | 1
Revolving Loans Amortized Cost Basis | 7 | 7 | 7
Total | 145 | 152 | 157
Special Mention [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 6 |  |
2024 | 16 | 15 | 16
2023 | 5 | 3 | 7
2022 | 10 | 8 | 1
2021 | 27 | 11 | 8
2020 |  | 1 | 1
Prior | 13 | 4 | 4
Revolving Loans Amortized Cost Basis | 0 |  | 0
Total | 77 | 42 | 37
Special Mention [Member] | C&I [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 5 |  |
2024 | 3 | 7 | 9
2023 | 1 |  | 1
2022 | 1 | 1 |
2021 | 15 |  |
2020 |  | 1 |
Prior | 1 |  |
Total | 26 | 9 | 10
Special Mention [Member] | Municipal [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2022 | 1 |  |
Prior | 8 |  |
Total | 9 |  | 0
Special Mention [Member] | Agriculture [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
Total | 3 |  |
Special Mention [Member] | Construction & Development [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 1 |  |
2024 |  | 1 | 2
2023 |  |  | 0
2021 |  |  | 0
Total | 1 | 1 | 2
Special Mention [Member] | Non-Owner Occupied CRE [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2024 |  | 4 |
2023 | 2 | 2 |
2022 | 6 | 1 |
2021 | 3 | 1 | 1
Prior | 1 | 1 | 1
Total | 12 | 9 | 3
Special Mention [Member] | Owner Occupied CRE [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2024 | 9 | 2 | 2
2023 | 1 |  | 5
2022 | 1 | 5 |
2021 | 7 | 7 | 5
2020 |  |  | 1
Prior | 1 | 1 | 1
Total | 19 | 15 | 14
Special Mention [Member] | Residential [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2024 | 4 | 1 | 2
2023 | 1 | 1 | 1
2022 | 1 | 1 | 1
2021 | 2 | 3 | 2
Prior | 2 | 2 | 2
Revolving Loans Amortized Cost Basis |  | 0 | 0
Total | 10 | 8 | 8
Substandard [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 26 |  |
2024 | 20 | 40 | 22
2023 | 23 | 29 | 21
2022 | 53 | 57 | 65
2021 | 21 | 23 | 25
2020 |  | 16 | 16
Prior | 30 | 25 | 40
Revolving Loans Amortized Cost Basis | 3 | 2 | 4
Total | 176 | 192 | 193
Substandard [Member] | C&I [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 7 |  |
2024 | 3 | 12 | 5
2023 | 2 | 3 | 3
2022 | 2 | 4 | 3
2021 |  | 1 | 1
2020 |  |  | 1
Prior | 0 | 1 | 2
Total | 14 | 21 | 15
Substandard [Member] | Municipal [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2021 |  |  | 0
Total |  |  | 0
Substandard [Member] | Agriculture [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 1 |  |
2024 | 1 | 3 | 3
2022 | 1 | 1 |
Total |  | 4 | 3
Substandard [Member] | Construction & Development [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 6 |  |
2024 | 6 | 7 | 5
2023 | 1 | 1 | 2
2022 | 1 | 1 | 1
2021 | 1 | 1 | 0
Total | 15 | 10 | 8
Substandard [Member] | Farm [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 1 |  |
2024 |  | 1 |
2023 |  | 1 | 1
2022 | 4 | 4 | 4
2021 | 1 |  |
2020 |  | 4 | 4
Prior | 4 | 1 | 1
Total | 10 | 11 | 10
Substandard [Member] | Non-Owner Occupied CRE [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 7 |  |
2024 |  | 10 | 3
2023 | 3 | 2 | 3
2022 | 2 | 3 | 1
2021 | 9 | 6 | 7
2020 |  | 7 | 6
Prior | 4 | 3 | 15
Total | 25 | 31 | 35
Substandard [Member] | Owner Occupied CRE [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 1 |  |
2024 |  | 1 | 2
2023 | 8 | 14 | 4
2022 | 29 | 30 | 42
2021 | 7 | 10 | 13
2020 |  | 1 | 1
Prior | 8 | 8 | 11
Total | 53 | 64 | 73
Substandard [Member] | Residential [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2025 | 3 |  |
2024 | 9 | 5 | 4
2023 | 8 | 7 | 7
2022 | 12 | 12 | 12
2021 | 3 | 4 | 3
2020 |  | 4 | 4
Prior | 14 | 12 | 11
Revolving Loans Amortized Cost Basis | 3 | 2 | 4
Total | 52 | 46 | 45
Substandard [Member] | Auto [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2024 | 1 | 1 |
2023 | 1 | 1 | 1
2022 | 1 | 1 | 1
2021 |  | 1 | 1
Total | 3 | 4 | 3
Substandard [Member] | Non-Auto [Member] |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |
2022 | 1 | 1 | 1
Total | $ 1 | $ 1 | $ 1

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