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Fair value measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024 | Sep. 30, 2024
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Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | $ 121,788 |  | $ 110,363 |  |
Equity securities | 10,377 |  | 9,151 |  |
Short-term investments | 4,380 |  | 5,142 |  |
Other investments | 10,182 |  | 8,597 |  |
Securities lending collateral | 1,899 |  | 1,445 |  |
Separate account assets | 6,810 |  | 6,231 |  | $ 5,996
Market risk benefits | 666 |  | 607 |  |
Private equities | 16,734 |  | 14,769 |  |
Reserved alternative investment fund |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Equity securities | 5,110 |  | 4,978 |  |
Other Investments |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Other investments | 1,438 |  | 1,241 |  |
Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Private equities | 16,734 |  | 14,769 |  |
U.S. and local government securities |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 3,846 |  | 4,070 |  |
Non-U.S. |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 40,331 |  | 35,838 |  |
Corporate and asset-backed securities |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 47,451 |  | 43,207 |  |
Mortgage-backed securities |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 30,160 |  | 27,248 |  |
Level 1 | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 1,665 |  | 1,765 |  |
Equity securities | 5,153 | [1] | 4,053 | [2] |
Short-term investments | 2,376 |  | 3,156 |  |
Other investments | 638 | [3] | 573 | [4] |
Securities lending collateral | 0 |  | 0 |  |
Investment derivatives | 22 |  | 41 |  |
Derivatives designated as hedging instruments | 0 |  | 0 |  |
Other derivative instruments | 5 |  | 35 |  |
Separate account assets | 6,733 |  | 6,165 |  |
Total assets measured at fair value | 16,592 | [1],[3],[5] | 15,788 | [2],[4],[6] |
Investment derivatives | 173 |  | 303 |  |
Derivatives designated as hedging instruments | 0 |  | 0 |  |
Other derivative instruments, liability | 11 |  |  |  |
Market risk benefits | 0 | [7] | 0 | [8] |
Total liabilities measured at fair value | 184 |  | 303 |  |
Level 1 | U.S. and local government securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 1,665 |  | 1,765 |  |
Level 1 | Non-U.S. | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0 |  | 0 |  |
Level 1 | Corporate and asset-backed securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0 |  | 0 |  |
Level 1 | Mortgage-backed securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0 |  | 0 |  |
Level 2 | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 116,282 |  | 105,100 |  |
Equity securities | 0 | [1] | 0 | [2] |
Short-term investments | 1,962 |  | 1,972 |  |
Other investments | 8,106 | [3] | 6,783 | [4] |
Securities lending collateral | 1,899 |  | 1,445 |  |
Investment derivatives | 0 |  | 0 |  |
Derivatives designated as hedging instruments | 261 |  | 146 |  |
Other derivative instruments | 0 |  | 0 |  |
Separate account assets | 77 |  | 66 |  |
Total assets measured at fair value | 128,587 | [1],[3],[5] | 115,512 | [2],[4],[6] |
Investment derivatives | 0 |  | 0 |  |
Derivatives designated as hedging instruments | 183 |  | 116 |  |
Other derivative instruments, liability | 5 |  | 2 |  |
Market risk benefits | 0 | [7] | 0 | [8] |
Total liabilities measured at fair value | 188 |  | 118 |  |
Level 2 | U.S. and local government securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 2,181 |  | 2,305 |  |
Level 2 | Non-U.S. | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 39,729 |  | 35,234 |  |
Level 2 | Corporate and asset-backed securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 44,212 |  | 40,316 |  |
Level 2 | Mortgage-backed securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 30,160 |  | 27,245 |  |
Level 3 | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 3,841 |  | 3,498 |  |
Equity securities | 114 | [1] | 120 | [2] |
Short-term investments | 42 |  | 14 |  |
Other investments | 0 | [3] | 0 | [4] |
Securities lending collateral | 0 |  | 0 |  |
Investment derivatives | 0 |  | 0 |  |
Derivatives designated as hedging instruments | 0 |  | 0 |  |
Other derivative instruments | 0 |  | 0 |  |
Separate account assets | 0 |  | 0 |  |
Total assets measured at fair value | 3,997 | [1],[3],[5] | 3,632 | [2],[4],[6] |
Investment derivatives | 0 |  | 0 |  |
Derivatives designated as hedging instruments | 0 |  | 0 |  |
Other derivative instruments, liability | 0 |  | 0 |  |
Market risk benefits | 666 | [7] | 607 | [8] |
Total liabilities measured at fair value | 666 |  | 607 |  |
Level 3 | U.S. and local government securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0 |  | 0 |  |
Level 3 | Non-U.S. | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 602 |  | 604 |  |
Level 3 | Corporate and asset-backed securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 3,239 |  | 2,891 |  |
Level 3 | Mortgage-backed securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0 |  | 3 |  |
Total Level 1, Level 2, and Level 3 | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 121,788 |  | 110,363 |  |
Equity securities | 5,267 | [1] | 4,173 | [2] |
Short-term investments | 4,380 |  | 5,142 |  |
Other investments | 8,744 | [3] | 7,356 | [4] |
Securities lending collateral | 1,899 |  | 1,445 |  |
Investment derivatives | 22 |  | 41 |  |
Derivatives designated as hedging instruments | 261 |  | 146 |  |
Other derivative instruments | 5 |  | 35 |  |
Separate account assets | 6,810 |  | 6,231 |  |
Total assets measured at fair value | 149,176 | [1],[3],[5] | 134,932 | [2],[4],[6] |
Investment derivatives | 173 |  | 303 |  |
Derivatives designated as hedging instruments | 183 |  | 116 |  |
Other derivative instruments, liability | 16 |  | 2 |  |
Market risk benefits | 666 | [7] | 607 | [8] |
Total liabilities measured at fair value | 1,038 |  | 1,028 |  |
Total Level 1, Level 2, and Level 3 | U.S. and local government securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 3,846 |  | 4,070 |  |
Total Level 1, Level 2, and Level 3 | Non-U.S. | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 40,331 |  | 35,838 |  |
Total Level 1, Level 2, and Level 3 | Corporate and asset-backed securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 47,451 |  | 43,207 |  |
Total Level 1, Level 2, and Level 3 | Mortgage-backed securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | $ 30,160 |  | $ 27,248 |  |
[1] | Excluded from the table above is a fund of $5,110 million, measured using NAV as a practical expedient.
[2] | Excluded from the table above is a fund of $4,978 million, measured using NAV as a practical expedient.
[3] | Excluded from the table above are other investments of $1,438 million, principally policy loans, measured using NAV as a practical expedient.
[4] | Excluded from the table above are other investments of $1,241 million, principally policy loans, measured using NAV as a practical expedient.
[5] | Excluded from the table above are private equities of $16,734 million, measured using NAV as a practical expedient.
[6] | Excluded from the table above are private equities of $14,769 million, measured using NAV as a practical expedient.
[7] | Refer to Note 11 for additional information on Market risk benefits.
[8] | Refer to Note 11 for additional information on Market risk benefits.

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