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Investment securities (Tables) | 6 Months Ended
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Jun. 30, 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
June 30, 2024 |  |  |  |  |  |  |
Investment securities available for sale: |  |  |  |  |  |  |
U.S. Treasury and federal agencies | $ | 7,819 |  |  | $ | 2 |  |  | $ | 85 |  |  | $ | 7,736 |
Mortgage-backed securities: |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |
Commercial | 2,101 |  |  | 4 |  |  | 16 |  |  | 2,089 |
Residential | 4,108 |  |  | 6 |  |  | 148 |  |  | 3,966 |
Other debt securities | 103 |  |  | — |  |  | 2 |  |  | 101 |
| 14,131 |  |  | 12 |  |  | 251 |  |  | 13,892 |
Investment securities held to maturity: |  |  |  |  |  |  |
U.S. Treasury and federal agencies | 1,010 |  |  | — |  |  | 30 |  |  | 980 |
Obligations of states and political subdivisions | 2,433 |  |  | — |  |  | 127 |  |  | 2,306 |
Mortgage-backed securities: |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |
Commercial | 2,037 |  |  | — |  |  | 157 |  |  | 1,880 |
Residential | 9,272 |  |  | — |  |  | 972 |  |  | 8,300 |
Privately issued | 40 |  |  | 7 |  |  | 5 |  |  | 42 |
Other debt securities | 1 |  |  | — |  |  | — |  |  | 1 |
| 14,793 |  |  | 7 |  |  | 1,291 |  |  | 13,509 |
Total debt securities | $ | 28,924 |  |  | $ | 19 |  |  | $ | 1,542 |  |  | $ | 27,401 |
Equity and other securities: |  |  |  |  |  |  |
Readily marketable equity — at fair value | $ | 272 |  |  | $ | 11 |  |  | $ | 3 |  |  | $ | 280 |
Other — at cost | 929 |  |  | — |  |  | — |  |  | 929 |
Total equity and other securities | $ | 1,201 |  |  | $ | 11 |  |  | $ | 3 |  |  | $ | 1,209 |
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 June 30, 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 | $ | 3,133 |  |  | $ | 3,093 |
Due after one year through five years | 4,789 |  |  | 4,744 |
Due after five years through ten years | — |  |  | — |
Due after ten years | — |  |  | — |
| 7,922 |  |  | 7,837 |
Mortgage-backed securities | 6,209 |  |  | 6,055 |
| $ | 14,131 |  |  | $ | 13,892 |
Debt securities held to maturity: |  |  |
Due in one year or less | $ | 588 |  |  | $ | 579 |
Due after one year through five years | 653 |  |  | 628 |
Due after five years through ten years | 1,392 |  |  | 1,332 |
Due after ten years | 811 |  |  | 748 |
| 3,444 |  |  | 3,287 |
Mortgage-backed securities | 11,349 |  |  | 10,222 |
| $ | 14,793 |  |  | $ | 13,509 |
Investment Securities in Continuous Unrealized Loss Position | A summary of investment securities that as of June 30, 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
June 30, 2024 |  |  |  |  |  |  |
Investment securities available for sale: |  |  |  |  |  |  |
U.S. Treasury and federal agencies | $ | 2,586 |  |  | $ | 15 |  |  | $ | 4,400 |  |  | $ | 70 |
Mortgage-backed securities: |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |
Commercial | 1,061 |  |  | 10 |  |  | 317 |  |  | 6 |
Residential | 1,129 |  |  | 11 |  |  | 1,874 |  |  | 137 |
Other debt securities | 10 |  |  | — |  |  | 64 |  |  | 2 |
| 4,786 |  |  | 36 |  |  | 6,655 |  |  | 215 |
Investment securities held to maturity: |  |  |  |  |  |  |
U.S. Treasury and federal agencies | — |  |  | — |  |  | 980 |  |  | 30 |
Obligations of states and political subdivisions | 45 |  |  | 1 |  |  | 2,214 |  |  | 126 |
Mortgage-backed securities: |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |
Commercial | — |  |  | — |  |  | 1,880 |  |  | 157 |
Residential | 790 |  |  | 13 |  |  | 7,510 |  |  | 959 |
Privately issued | — |  |  | — |  |  | 31 |  |  | 5 |
| 835 |  |  | 14 |  |  | 12,615 |  |  | 1,277 |
Total | $ | 5,621 |  |  | $ | 50 |  |  | $ | 19,270 |  |  | $ | 1,492 |
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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