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Fair value measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions | Mar. 31, 2024 | Dec. 31, 2023 | Mar. 31, 2023
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Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | $ 108,289 |  | $ 106,571 |  |
Equity securities | 3,769 |  | 3,455 |  |
Short-term investments | 5,107 |  | 4,551 |  |
Other Investments | 6,216 |  | 5,527 |  |
Securities lending collateral | 1,708 |  | 1,299 |  |
Separate account assets | 5,864 |  | 5,573 |  | $ 5,300
Market risk benefits | 611 |  | 771 |  |
Private equities | 14,281 |  | 14,078 |  |
Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Private equities | 14,281 |  | 14,078 |  |
Policy Loans |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Other Investments | 736 |  | 702 |  |
U.S. Treasury / Agency |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 2,899 |  | 3,590 |  |
Non-U.S. |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 36,145 |  | 35,164 |  |
Corporate and asset-backed securities |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 43,447 |  | 42,830 |  |
Mortgage-backed securities |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 23,755 |  | 22,058 |  |
Municipal |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 2,043 |  | 2,929 |  |
Level 1 | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 2,251 |  | 2,911 |  |
Equity securities | 3,668 |  | 3,368 |  |
Short-term investments | 3,292 |  | 1,915 |  |
Other Investments | 583 | [1] | 589 | [2] |
Securities lending collateral | 0 |  | 0 |  |
Investment derivatives | 28 |  | 54 |  |
Derivatives designated as hedging instruments | 0 |  | 0 |  |
Other derivative instruments | 1 |  |  |  |
Separate account assets | 5,775 |  | 5,482 |  |
Total assets measured at fair value | 15,598 | [1],[3] | 14,319 | [2],[4] |
Investment derivatives | 144 |  | 136 |  |
Derivatives designated as hedging instruments | 0 |  | 0 |  |
Other derivative instruments, liability | 22 |  | 37 |  |
Market risk benefits | 0 | [5] | 0 | [6] |
Total liabilities measured at fair value | 166 |  | 173 |  |
Level 1 | U.S. Treasury / Agency | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 2,251 |  | 2,911 |  |
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 1 | Municipal | 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 | 102,655 |  | 100,339 |  |
Equity securities | 0 |  | 0 |  |
Short-term investments | 1,810 |  | 2,633 |  |
Other Investments | 4,897 | [1] | 4,236 | [2] |
Securities lending collateral | 1,708 |  | 1,299 |  |
Investment derivatives | 0 |  | 0 |  |
Derivatives designated as hedging instruments | 149 |  | 136 |  |
Other derivative instruments | 0 |  |  |  |
Separate account assets | 89 |  | 91 |  |
Total assets measured at fair value | 111,308 | [1],[3] | 108,734 | [2],[4] |
Investment derivatives | 0 |  | 0 |  |
Derivatives designated as hedging instruments | 110 |  | 128 |  |
Other derivative instruments, liability | 6 |  | 5 |  |
Market risk benefits | 0 | [5] | 0 | [6] |
Total liabilities measured at fair value | 116 |  | 133 |  |
Level 2 | U.S. Treasury / Agency | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 648 |  | 679 |  |
Level 2 | Non-U.S. | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 35,427 |  | 34,472 |  |
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 | 40,789 |  | 40,208 |  |
Level 2 | Mortgage-backed securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 23,748 |  | 22,051 |  |
Level 2 | Municipal | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 2,043 |  | 2,929 |  |
Level 3 | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 3,383 |  | 3,321 |  |
Equity securities | 101 |  | 87 |  |
Short-term investments | 5 |  | 3 |  |
Other Investments | 0 | [1] | 0 | [2] |
Securities lending collateral | 0 |  | 0 |  |
Investment derivatives | 0 |  | 0 |  |
Derivatives designated as hedging instruments | 0 |  | 0 |  |
Other derivative instruments | 0 |  |  |  |
Separate account assets | 0 |  | 0 |  |
Total assets measured at fair value | 3,489 | [1],[3] | 3,411 | [2],[4] |
Investment derivatives | 0 |  | 0 |  |
Derivatives designated as hedging instruments | 0 |  | 0 |  |
Other derivative instruments, liability | 0 |  | 0 |  |
Market risk benefits | 611 | [5] | 771 | [6] |
Total liabilities measured at fair value | 611 |  | 771 |  |
Level 3 | U.S. Treasury / Agency | 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 | 718 |  | 692 |  |
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 | 2,658 |  | 2,622 |  |
Level 3 | Mortgage-backed securities | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 7 |  | 7 |  |
Level 3 | Municipal | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0 |  | 0 |  |
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 | 108,289 |  | 106,571 |  |
Equity securities | 3,769 |  | 3,455 |  |
Short-term investments | 5,107 |  | 4,551 |  |
Other Investments | 5,480 | [1] | 4,825 | [2] |
Securities lending collateral | 1,708 |  | 1,299 |  |
Investment derivatives | 28 |  | 54 |  |
Derivatives designated as hedging instruments | 149 |  | 136 |  |
Other derivative instruments | 1 |  |  |  |
Separate account assets | 5,864 |  | 5,573 |  |
Total assets measured at fair value | 130,395 | [1],[3] | 126,464 | [2],[4] |
Investment derivatives | 144 |  | 136 |  |
Derivatives designated as hedging instruments | 110 |  | 128 |  |
Other derivative instruments, liability | 28 |  | 42 |  |
Market risk benefits | 611 | [5] | 771 | [6] |
Total liabilities measured at fair value | 893 |  | 1,077 |  |
Total Level 1, Level 2, and Level 3 | U.S. Treasury / Agency | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 2,899 |  | 3,590 |  |
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 | 36,145 |  | 35,164 |  |
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 | 43,447 |  | 42,830 |  |
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 | 23,755 |  | 22,058 |  |
Total Level 1, Level 2, and Level 3 | Municipal | Fair Value, Recurring |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | $ 2,043 |  | $ 2,929 |  |
[1] | Excluded from the table above are other investments of $736 million, principally policy loans at March 31, 2024, measured using NAV as a practical expedient.
[2] | Excluded from the table above are other investments of $702 million, principally policy loans at December 31, 2023, measured using NAV as a practical expedient.
[3] | Excluded from the table above are Private equities of $14,281 million at March 31, 2024, measured using NAV as a practical expedient.
[4] | Excluded from the table above are Private equities of $14,078 million at December 31, 2023, measured using NAV as a practical expedient.
[5] | Refer to Note 10 for additional information on Market risk benefits.
[6] | Refer to Note 10 for additional information on Market risk benefits.

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