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Investment securities (Tables) | 3 Months Ended
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Mar. 31, 2025
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 (a) |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Estimated Fair Value
March 31, 2025 |  |  |  |  |  |  |
Investment securities available for sale: |  |  |  |  |  |  |
U.S. Treasury | $ | 8,065 |  |  | $ | 31 |  |  | $ | 11 |  |  | $ | 8,085 |
Mortgage-backed securities: |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |
Commercial | 4,316 |  |  | 35 |  |  | 11 |  |  | 4,340 |
Residential | 8,422 |  |  | 47 |  |  | 99 |  |  | 8,370 |
Other | 4 |  |  | — |  |  | — |  |  | 4 |
| 20,807 |  |  | 113 |  |  | 121 |  |  | 20,799 |
Investment securities held to maturity: |  |  |  |  |  |  |
U.S. Treasury | 442 |  |  | — |  |  | 10 |  |  | 432 |
Mortgage-backed securities: |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |
Commercial | 2,035 |  |  | — |  |  | 114 |  |  | 1,921 |
Residential | 8,547 |  |  | — |  |  | 800 |  |  | 7,747 |
Privately issued | 36 |  |  | 8 |  |  | — |  |  | 44 |
State and political subdivisions | 2,291 |  |  | — |  |  | 128 |  |  | 2,163 |
Other | 1 |  |  | — |  |  | — |  |  | 1 |
| 13,352 |  |  | 8 |  |  | 1,052 |  |  | 12,308 |
Total debt securities | $ | 34,159 |  |  | $ | 121 |  |  | $ | 1,173 |  |  | $ | 33,107 |
Equity and other securities: |  |  |  |  |  |  |
Readily marketable equity — at fair value | $ | 280 |  |  | $ | 2 |  |  | $ | 2 |  |  | $ | 280 |
Other — at cost | 706 |  |  | — |  |  | — |  |  | 706 |
Total equity and other securities | $ | 986 |  |  | $ | 2 |  |  | $ | 2 |  |  | $ | 986 |
December 31, 2024 |  |  |  |  |  |  |
Investment securities available for sale: |  |  |  |  |  |  |
U.S. Treasury | $ | 7,945 |  |  | $ | 13 |  |  | $ | 27 |  |  | $ | 7,931 |
Mortgage-backed securities: |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |
Commercial | 3,739 |  |  | 8 |  |  | 45 |  |  | 3,702 |
Residential | 7,368 |  |  | 13 |  |  | 167 |  |  | 7,214 |
Other | 2 |  |  | — |  |  | — |  |  | 2 |
| 19,054 |  |  | 34 |  |  | 239 |  |  | 18,849 |
Investment securities held to maturity: |  |  |  |  |  |  |
U.S. Treasury | 1,015 |  |  | — |  |  | 14 |  |  | 1,001 |
Mortgage-backed securities: |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |
Commercial | 2,034 |  |  | — |  |  | 157 |  |  | 1,877 |
Residential | 8,773 |  |  | — |  |  | 961 |  |  | 7,812 |
Privately issued | 37 |  |  | 9 |  |  | — |  |  | 46 |
State and political subdivisions | 2,335 |  |  | — |  |  | 117 |  |  | 2,218 |
Other | 1 |  |  | — |  |  | — |  |  | 1 |
| 14,195 |  |  | 9 |  |  | 1,249 |  |  | 12,955 |
Total debt securities | $ | 33,249 |  |  | $ | 43 |  |  | $ | 1,488 |  |  | $ | 31,804 |
Equity and other securities: |  |  |  |  |  |  |
Readily marketable equity — at fair value | $ | 235 |  |  | $ | 3 |  |  | $ | 3 |  |  | $ | 235 |
Other — at cost | 772 |  |  | — |  |  | — |  |  | 772 |
Total equity and other securities | $ | 1,007 |  |  | $ | 3 |  |  | $ | 3 |  |  | $ | 1,007 |
__________________________________________________________________________________ (a)Amortized cost balances of debt securities exclude accrued interest receivable of $168 million and $176 million at March 31, 2025 and December 31, 2024, respectively, which is included as Accrued interest and other assets in the Company's Consolidated Balance Sheet.
Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity | At March 31, 2025, 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 | $ | 3,155 |  |  | $ | 3,154 |
Due after one year through five years | 4,914 |  |  | 4,935 |
Due after five years through ten years | — |  |  | — |
Due after ten years | — |  |  | — |
| 8,069 |  |  | 8,089 |
Mortgage-backed securities | 12,738 |  |  | 12,710 |
| $ | 20,807 |  |  | $ | 20,799 |
Debt securities held to maturity: |  |  |
Due in one year or less | $ | 76 |  |  | $ | 76 |
Due after one year through five years | 614 |  |  | 601 |
Due after five years through ten years | 1,459 |  |  | 1,396 |
Due after ten years | 585 |  |  | 523 |
| 2,734 |  |  | 2,596 |
Mortgage-backed securities | 10,618 |  |  | 9,712 |
| $ | 13,352 |  |  | $ | 12,308 |
Investment Securities in Continuous Unrealized Loss Position | A summary of investment securities that as of March 31, 2025 and December 31, 2024 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, 2025 |  |  |  |  |  |  |
Investment securities available for sale: |  |  |  |  |  |  |
U.S. Treasury | $ | 814 |  |  | $ | 1 |  |  | $ | 2,014 |  |  | $ | 10 |
Mortgage-backed securities: |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |
Commercial | 1,362 |  |  | 11 |  |  | 26 |  |  | — |
Residential | 1,349 |  |  | 10 |  |  | 1,548 |  |  | 89 |
Other | 1 |  |  | — |  |  | 2 |  |  | — |
| 3,526 |  |  | 22 |  |  | 3,590 |  |  | 99 |
Investment securities held to maturity: |  |  |  |  |  |  |
U.S. Treasury | 50 |  |  | — |  |  | 382 |  |  | 10 |
Mortgage-backed securities: |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |
Commercial | — |  |  | — |  |  | 1,921 |  |  | 114 |
Residential | 764 |  |  | 5 |  |  | 6,761 |  |  | 795 |
State and political subdivisions | 40 |  |  | 1 |  |  | 2,070 |  |  | 127 |
| 854 |  |  | 6 |  |  | 11,134 |  |  | 1,046 |
Total | $ | 4,380 |  |  | $ | 28 |  |  | $ | 14,724 |  |  | $ | 1,145 |
December 31, 2024 |  |  |  |  |  |  |
Investment securities available for sale: |  |  |  |  |  |  |
U.S. Treasury | $ | 1,971 |  |  | $ | 9 |  |  | $ | 2,554 |  |  | $ | 18 |
Mortgage-backed securities: |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |
Commercial | 2,566 |  |  | 45 |  |  | 64 |  |  | — |
Residential | 4,429 |  |  | 53 |  |  | 1,623 |  |  | 114 |
Other | — |  |  | — |  |  | 2 |  |  | — |
| 8,966 |  |  | 107 |  |  | 4,243 |  |  | 132 |
Investment securities held to maturity: |  |  |  |  |  |  |
U.S. Treasury | 50 |  |  | — |  |  | 951 |  |  | 14 |
Mortgage-backed securities: |  |  |  |  |  |  |
Government issued or guaranteed: |  |  |  |  |  |  |
Commercial | — |  |  | — |  |  | 1,877 |  |  | 157 |
Residential | 996 |  |  | 19 |  |  | 6,811 |  |  | 942 |
State and political subdivisions | 39 |  |  | 1 |  |  | 2,131 |  |  | 116 |
| 1,085 |  |  | 20 |  |  | 11,770 |  |  | 1,229 |
Total | $ | 10,051 |  |  | $ | 127 |  |  | $ | 16,013 |  |  | $ | 1,361 |

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