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Investment securities (Tables) | 3 Months Ended
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Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract] |
Amortized Cost and Estimated Fair Value of Investment Securities | The amortized cost and estimated fair value of investment securities were as follows:
(Dollars in millions) |  | Amortized Cost |  |  | Gross Unrealized Gains |  |  | Gross Unrealized Losses |  |  | Estimated Fair Value |
March 31, 2024 |  |  |  |  |  |  |  |  |  |  |  |
Investment securities available for sale: |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury and federal agencies |  | $ | 7,818 |  |  | $ | — |  |  | $ | 99 |  |  | $ | 7,719 |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |  |  |  |  |  |
Commercial |  |  | 1,355 |  |  |  | 1 |  |  |  | 13 |  |  |  | 1,343 |
Residential |  |  | 3,053 |  |  |  | — |  |  |  | 143 |  |  |  | 2,910 |
Other debt securities |  |  | 171 |  |  |  | — |  |  |  | 9 |  |  |  | 162 |
|  |  | 12,397 |  |  |  | 1 |  |  |  | 264 |  |  |  | 12,134 |
Investment securities held to maturity: |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury and federal agencies |  |  | 1,007 |  |  |  | — |  |  |  | 33 |  |  |  | 974 |
Obligations of states and political subdivisions |  |  | 2,466 |  |  |  | — |  |  |  | 94 |  |  |  | 2,372 |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |  |  |  |  |  |
Commercial |  |  | 2,035 |  |  |  | — |  |  |  | 154 |  |  |  | 1,881 |
Residential |  |  | 9,527 |  |  |  | — |  |  |  | 935 |  |  |  | 8,592 |
Privately issued |  |  | 41 |  |  |  | 9 |  |  |  | 6 |  |  |  | 44 |
Other debt securities |  |  | 2 |  |  |  | — |  |  |  | — |  |  |  | 2 |
|  |  | 15,078 |  |  |  | 9 |  |  |  | 1,222 |  |  |  | 13,865 |
Total debt securities |  | $ | 27,475 |  |  | $ | 10 |  |  | $ | 1,486 |  |  | $ | 25,999 |
Equity and other securities: |  |  |  |  |  |  |  |  |  |  |  |
Readily marketable equity — at fair value |  | $ | 351 |  |  | $ | 8 |  |  | $ | 3 |  |  | $ | 356 |
Other — at cost |  |  | 928 |  |  |  | — |  |  |  | — |  |  |  | 928 |
Total equity and other securities |  | $ | 1,279 |  |  | $ | 8 |  |  | $ | 3 |  |  | $ | 1,284 |
December 31, 2023 |  |  |  |  |  |  |  |  |  |  |  |
Investment securities available for sale: |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury and federal agencies |  | $ | 7,818 |  |  | $ | — |  |  | $ | 113 |  |  | $ | 7,705 |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |  |  |  |  |  |
Commercial |  |  | 425 |  |  |  | — |  |  |  | 9 |  |  |  | 416 |
Residential |  |  | 2,272 |  |  |  | — |  |  |  | 118 |  |  |  | 2,154 |
Other debt securities |  |  | 176 |  |  |  | — |  |  |  | 11 |  |  |  | 165 |
|  |  | 10,691 |  |  |  | — |  |  |  | 251 |  |  |  | 10,440 |
Investment securities held to maturity: |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury and federal agencies |  |  | 1,005 |  |  |  | — |  |  |  | 31 |  |  |  | 974 |
Obligations of states and political subdivisions |  |  | 2,501 |  |  |  | — |  |  |  | 67 |  |  |  | 2,434 |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |  |  |  |  |  |
Commercial |  |  | 2,033 |  |  |  | — |  |  |  | 130 |  |  |  | 1,903 |
Residential |  |  | 9,747 |  |  |  | 4 |  |  |  | 802 |  |  |  | 8,949 |
Privately issued |  |  | 42 |  |  |  | 9 |  |  |  | 5 |  |  |  | 46 |
Other debt securities |  |  | 2 |  |  |  | — |  |  |  | — |  |  |  | 2 |
|  |  | 15,330 |  |  |  | 13 |  |  |  | 1,035 |  |  |  | 14,308 |
Total debt securities |  | $ | 26,021 |  |  | $ | 13 |  |  | $ | 1,286 |  |  | $ | 24,748 |
Equity and other securities: |  |  |  |  |  |  |  |  |  |  |  |
Readily marketable equity — at fair value |  | $ | 266 |  |  | $ | 5 |  |  | $ | 3 |  |  | $ | 268 |
Other — at cost |  |  | 859 |  |  |  | — |  |  |  | — |  |  |  | 859 |
Total equity and other securities |  | $ | 1,125 |  |  | $ | 5 |  |  | $ | 3 |  |  | $ | 1,127 |
Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity | At March 31, 2024, the amortized cost and estimated fair value of debt securities by contractual maturity were as follows:
(Dollars in millions) |  | Amortized Cost |  |  | Estimated Fair Value |
Debt securities available for sale: |  |  |  |  |  |
Due in one year or less |  | $ | 3,248 |  |  | $ | 3,209 |
Due after one year through five years |  |  | 4,691 |  |  |  | 4,628 |
Due after five years through ten years |  |  | 50 |  |  |  | 44 |
Due after ten years |  |  | — |  |  |  | — |
|  |  | 7,989 |  |  |  | 7,881 |
Mortgage-backed securities |  |  | 4,408 |  |  |  | 4,253 |
|  | $ | 12,397 |  |  | $ | 12,134 |
Debt securities held to maturity: |  |  |  |  |  |
Due in one year or less |  | $ | 588 |  |  | $ | 575 |
Due after one year through five years |  |  | 635 |  |  |  | 611 |
Due after five years through ten years |  |  | 1,369 |  |  |  | 1,333 |
Due after ten years |  |  | 883 |  |  |  | 829 |
|  |  | 3,475 |  |  |  | 3,348 |
Mortgage-backed securities |  |  | 11,603 |  |  |  | 10,517 |
|  | $ | 15,078 |  |  | $ | 13,865 |
Investment Securities in Continuous Unrealized Loss Position | A summary of investment securities that as of March 31, 2024 and December 31, 2023 had been in a continuous unrealized loss position for less than twelve months and those that had been in a continuous unrealized loss position for twelve months or longer follows:
|  | Less Than 12 Months |  |  | 12 Months or More |
(Dollars in millions) |  | Fair Value |  |  | Unrealized Losses |  |  | Fair Value |  |  | Unrealized Losses |
March 31, 2024 |  |  |  |  |  |  |  |  |  |  |  |
Investment securities available for sale: |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury and federal agencies |  | $ | 2,242 |  |  | $ | 10 |  |  | $ | 5,177 |  |  | $ | 89 |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |  |  |  |  |  |
Commercial |  |  | 765 |  |  |  | 6 |  |  |  | 393 |  |  |  | 7 |
Residential |  |  | 813 |  |  |  | 6 |  |  |  | 1,964 |  |  |  | 137 |
Other debt securities |  |  | — |  |  |  | — |  |  |  | 156 |  |  |  | 9 |
|  |  | 3,820 |  |  |  | 22 |  |  |  | 7,690 |  |  |  | 242 |
Investment securities held to maturity: |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury and federal agencies |  |  | 49 |  |  |  | 1 |  |  |  | 925 |  |  |  | 32 |
Obligations of states and political subdivisions |  |  | 43 |  |  |  | — |  |  |  | 2,284 |  |  |  | 94 |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |  |  |  |  |  |
Commercial |  |  | 172 |  |  |  | 9 |  |  |  | 1,709 |  |  |  | 145 |
Residential |  |  | 1,133 |  |  |  | 12 |  |  |  | 7,459 |  |  |  | 923 |
Privately issued |  |  | — |  |  |  | — |  |  |  | 33 |  |  |  | 6 |
|  |  | 1,397 |  |  |  | 22 |  |  |  | 12,410 |  |  |  | 1,200 |
Total |  | $ | 5,217 |  |  | $ | 44 |  |  | $ | 20,100 |  |  | $ | 1,442 |
December 31, 2023 |  |  |  |  |  |  |  |  |  |  |  |
Investment securities available for sale: |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury and federal agencies |  | $ | 229 |  |  | $ | 1 |  |  | $ | 7,474 |  |  | $ | 112 |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |  |  |  |  |  |
Commercial |  |  | 74 |  |  |  | 1 |  |  |  | 330 |  |  |  | 8 |
Residential |  |  | 151 |  |  |  | 2 |  |  |  | 1,959 |  |  |  | 116 |
Other debt securities |  |  | 6 |  |  |  | — |  |  |  | 154 |  |  |  | 11 |
|  |  | 460 |  |  |  | 4 |  |  |  | 9,917 |  |  |  | 247 |
Investment securities held to maturity: |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury and federal agencies |  |  | 50 |  |  |  | — |  |  |  | 924 |  |  |  | 31 |
Obligations of states and political subdivisions |  |  | 218 |  |  |  | 3 |  |  |  | 2,172 |  |  |  | 64 |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |  |  |  |  |  |
Commercial |  |  | 328 |  |  |  | 9 |  |  |  | 1,575 |  |  |  | 121 |
Residential |  |  | 955 |  |  |  | 11 |  |  |  | 7,139 |  |  |  | 791 |
Privately issued |  |  | — |  |  |  | — |  |  |  | 34 |  |  |  | 5 |
|  |  | 1,551 |  |  |  | 23 |  |  |  | 11,844 |  |  |  | 1,012 |
Total |  | $ | 2,011 |  |  | $ | 27 |  |  | $ | 21,761 |  |  | $ | 1,259 |

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