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Investments (Tables) | 9 Months Ended
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Sep. 30, 2025
Investments [Abstract] |
Amortized cost and fair value of investments in fixed maturities [Table Text Block] | The amortized cost and fair value of investments in fixed maturities classified as available for sale were as follows:
|  | Amortized Cost |  | Allowance for Expected Credit Losses |  | Gross Unrealized |  | Fair Value
(as of September 30, 2025, in millions) |  |  |  | Gains |  | Losses |
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities |  | $ | 4,084 |  |  | $ | — |  |  | $ | 15 |  |  | $ | 86 |  |  | $ | 4,013 |
Obligations of U.S. states, municipalities and political subdivisions: |  |  |  |  |  |  |  |  |  |
Local general obligation |  | 21,171 |  |  | — |  |  | 103 |  |  | 1,342 |  |  | 19,932 |
Revenue |  | 9,677 |  |  | — |  |  | 42 |  |  | 642 |  |  | 9,077 |
State general obligation |  | 1,019 |  |  | — |  |  | 5 |  |  | 55 |  |  | 969 |
Pre-refunded |  | 324 |  |  | — |  |  | 3 |  |  | 1 |  |  | 326 |
Total obligations of U.S. states, municipalities and political subdivisions |  | 32,191 |  |  | — |  |  | 153 |  |  | 2,040 |  |  | 30,304 |
Debt securities issued by foreign governments |  | 984 |  |  | — |  |  | 10 |  |  | 6 |  |  | 988 |
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities |  | 13,287 |  |  | — |  |  | 225 |  |  | 151 |  |  | 13,361 |
Corporate and all other bonds |  | 43,052 |  |  | 4 |  |  | 480 |  |  | 1,081 |  |  | 42,447 |
Total |  | $ | 93,598 |  |  | $ | 4 |  |  | $ | 883 |  |  | $ | 3,364 |  |  | $ | 91,113 |
|  | Amortized Cost |  | Allowance for Expected Credit Losses |  | Gross Unrealized |  | Fair Value
(as of December 31, 2024, in millions) |  |  |  | Gains |  | Losses |
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities |  | $ | 5,735 |  |  | $ | — |  |  | $ | 4 |  |  | $ | 169 |  |  | $ | 5,570 |
Obligations of U.S. states, municipalities and political subdivisions: |  |  |  |  |  |  |  |  |  |
Local general obligation |  | 18,604 |  |  | — |  |  | 23 |  |  | 1,604 |  |  | 17,023 |
Revenue |  | 9,268 |  |  | — |  |  | 16 |  |  | 704 |  |  | 8,580 |
State general obligation |  | 1,081 |  |  | — |  |  | 2 |  |  | 73 |  |  | 1,010 |
Pre-refunded |  | 573 |  |  | — |  |  | 2 |  |  | 3 |  |  | 572 |
Total obligations of U.S. states, municipalities and political subdivisions |  | 29,526 |  |  | — |  |  | 43 |  |  | 2,384 |  |  | 27,185 |
Debt securities issued by foreign governments |  | 917 |  |  | — |  |  | 5 |  |  | 13 |  |  | 909 |
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities |  | 12,888 |  |  | — |  |  | 53 |  |  | 336 |  |  | 12,605 |
Corporate and all other bonds |  | 39,211 |  |  | 2 |  |  | 118 |  |  | 1,930 |  |  | 37,397 |
Total |  | $ | 88,277 |  |  | $ | 2 |  |  | $ | 223 |  |  | $ | 4,832 |  |  | $ | 83,666 |
Cost and fair value of investments in equity securities [Table Text Block] | The cost and fair value of investments in equity securities were as follows:
(as of September 30, 2025, in millions) |  | Cost |  | Gross Gains |  | Gross Losses |  | Fair Value
Common stock |  | $ | 462 |  |  | $ | 193 |  |  | $ | 6 |  |  | $ | 649 |
Non-redeemable preferred stock |  | 44 |  |  | 5 |  |  | 6 |  |  | 43 |
Total |  | $ | 506 |  |  | $ | 198 |  |  | $ | 12 |  |  | $ | 692 |
(as of December 31, 2024, in millions) |  | Cost |  | Gross Gains |  | Gross Losses |  | Fair Value
Common stock |  | $ | 500 |  |  | $ | 150 |  |  | $ | 11 |  |  | $ | 639 |
Non-redeemable preferred stock |  | 44 |  |  | 4 |  |  | — |  |  | 48 |
Total |  | $ | 544 |  |  | $ | 154 |  |  | $ | 11 |  |  | $ | 687 |
Unrealized investment losses [Table Text Block] | The following tables summarize, for all fixed maturities classified as available for sale in an unrealized loss position as of September 30, 2025 and December 31, 2024, the aggregate fair value and gross unrealized loss by the length of time those securities have been continuously in an unrealized loss position. The fair value amounts reported in the tables are estimates that are prepared using the process described in note 4 herein and in note 4 of the notes to the consolidated financial statements in the Company’s 2024 Annual Report. The Company also relies upon estimates of several factors in its review and evaluation of individual investments, using the process described in note 1 of the notes to the consolidated financial statements in the Company’s 2024 Annual Report to determine whether a credit loss impairment exists.
|  | Less than 12 months |  | 12 months or longer |  | Total
(as of September 30, 2025, in millions) |  | Fair Value |  | Gross Unrealized Losses |  | Fair Value |  | Gross Unrealized Losses |  | Fair Value |  | Gross Unrealized Losses
Fixed maturities |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities |  | $ | 192 |  |  | $ | — |  |  | $ | 2,067 |  |  | $ | 86 |  |  | $ | 2,259 |  |  | $ | 86 |
Obligations of U.S. states, municipalities and political subdivisions |  | 6,006 |  |  | 162 |  |  | 14,917 |  |  | 1,878 |  |  | 20,923 |  |  | 2,040 |
Debt securities issued by foreign governments |  | 52 |  |  | — |  |  | 327 |  |  | 6 |  |  | 379 |  |  | 6 |
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities |  | 1,031 |  |  | 7 |  |  | 1,773 |  |  | 144 |  |  | 2,804 |  |  | 151 |
Corporate and all other bonds |  | 1,896 |  |  | 10 |  |  | 19,447 |  |  | 1,071 |  |  | 21,343 |  |  | 1,081 |
Total |  | $ | 9,177 |  |  | $ | 179 |  |  | $ | 38,531 |  |  | $ | 3,185 |  |  | $ | 47,708 |  |  | $ | 3,364 |
|  | Less than 12 months |  | 12 months or longer |  | Total
(as of December 31, 2024, in millions) |  | Fair Value |  | Gross Unrealized Losses |  | Fair Value |  | Gross Unrealized Losses |  | Fair Value |  | Gross Unrealized Losses
Fixed maturities |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities |  | $ | 557 |  |  | $ | 1 |  |  | $ | 2,830 |  |  | $ | 168 |  |  | $ | 3,387 |  |  | $ | 169 |
Obligations of U.S. states, municipalities and political subdivisions |  | 8,584 |  |  | 160 |  |  | 15,007 |  |  | 2,224 |  |  | 23,591 |  |  | 2,384 |
Debt securities issued by foreign governments |  | 113 |  |  | 1 |  |  | 454 |  |  | 12 |  |  | 567 |  |  | 13 |
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities |  | 7,359 |  |  | 148 |  |  | 1,419 |  |  | 188 |  |  | 8,778 |  |  | 336 |
Corporate and all other bonds |  | 7,341 |  |  | 144 |  |  | 21,999 |  |  | 1,786 |  |  | 29,340 |  |  | 1,930 |
Total |  | $ | 23,954 |  |  | $ | 454 |  |  | $ | 41,709 |  |  | $ | 4,378 |  |  | $ | 65,663 |  |  | $ | 4,832 |
Gross unrealized investment losses on securities continuously in an unrealized loss position of greater than 20% of amortized cost by length of time [Table Text Block] | The following tables summarize, for all fixed maturities reported at fair value for which fair value was less than 80% of amortized cost as of September 30, 2025 and December 31, 2024, the gross unrealized investment loss by length of time those securities have continuously been in an unrealized loss position of greater than 20% of amortized cost:
|  | Period For Which Fair Value is Less Than 80% of Amortized Cost
(as of September 30, 2025, in millions) |  | 3 months or less |  | Greater than 3 months, 6 months or less |  | Greater than 6 months, 12 months or less |  | Greater than 12 months |  | Total
Fixed maturities |  |  |  |  |  |  |  |  |  |
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Obligations of U.S. states, municipalities and political subdivisions |  | — |  |  | 2 |  |  | 161 |  |  | 641 |  |  | 804 |
Debt securities issued by foreign governments |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Corporate and all other bonds |  | 2 |  |  | — |  |  | 4 |  |  | 1 |  |  | 7 |
Total |  | $ | 2 |  |  | $ | 2 |  |  | $ | 165 |  |  | $ | 642 |  |  | $ | 811 |
|  | Period For Which Fair Value is Less Than 80% of Amortized Cost
(as of December 31, 2024, in millions) |  | 3 months or less |  | Greater than 3 months, 6 months or less |  | Greater than 6 months, 12 months or less |  | Greater than 12 months |  | Total
Fixed maturities |  |  |  |  |  |  |  |  |  |
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Obligations of U.S. states, municipalities and political subdivisions |  | 366 |  |  | — |  |  | 43 |  |  | 635 |  |  | 1,044 |
Debt securities issued by foreign governments |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities |  | 58 |  |  | — |  |  | — |  |  | — |  |  | 58 |
Corporate and all other bonds |  | 13 |  |  | — |  |  | — |  |  | 3 |  |  | 16 |
Total |  | $ | 437 |  |  | $ | — |  |  | $ | 43 |  |  | $ | 638 |  |  | $ | 1,118 |
Changes in the allowance for expected credit losses on fixed maturities classified as available for sale [Table Text Block] | The following tables present changes in the allowance for expected credit losses on fixed maturities classified as available for sale for the category of Corporate and All Other Bonds (no other categories of fixed maturities currently have an allowance for expected credit losses):
|  | Fixed Maturities
|  | Corporate and All Other Bonds
|  | As of and For the Three Months Ended |  |
(in millions) |  | September 30, 2025 |  |  |  | September 30, 2024
Balance, beginning of period |  | $ | 4 |  |  |  |  | $ | 1 |  |  |
Additions for expected credit losses on securities where no credit losses were previously recognized |  | — |  |  |  |  | — |  |  |
Additions (reductions) for expected credit losses on securities where credit losses were previously recognized |  | — |  |  |  |  | (1) |  |  |
Reductions due to sales/defaults of credit-impaired securities |  | — |  |  |  |  | — |  |  |
Reductions for impairments of securities which the Company intends to sell or more likely than not will be required to sell |  | — |  |  |  |  | — |  |  |
Balance, end of period |  | $ | 4 |  |  |  |  | $ | — |  |  |
|  | Fixed Maturities
|  | Corporate and All Other Bonds
|  | As of and For the Nine Months Ended
(in millions) |  | September 30, 2025 |  | September 30, 2024
Balance, beginning of period |  | $ | 2 |  |  |  |  | $ | 5 |
Additions for expected credit losses on securities where no credit losses were previously recognized |  | 2 |  |  |  |  | 3 |
Additions (reductions) for expected credit losses on securities where credit losses were previously recognized |  | — |  |  |  |  | (1) |
Reductions due to sales/defaults of credit-impaired securities |  | — |  |  |  |  | (7) |
Reductions for impairments of securities which the Company intends to sell or more likely than not will be required to sell |  | — |  |  |  |  | — |
Balance, end of period |  | $ | 4 |  |  |  |  | $ | — |

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