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Fair Value Measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Detail) - USD ($) $ in Millions | Jun. 30, 2021 | Dec. 31, 2020
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Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | $ 92,163 |  | $ 90,699 |
Equity securities, at fair value | 4,607 |  | 4,027 |
Short-term investments | 4,470 |  | 4,345 |
Other investments, at fair value | 9,457 |  | 7,945 |
Securities lending collateral | 2,369 |  | 1,844 |
U.S. Treasury / Agency |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 2,478 |  | 2,670 |
Non-U.S. |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 26,412 |  | 26,354 |
Corporate and asset-backed securities |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 37,575 |  | 36,331 |
Mortgage-backed securities |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 19,553 |  | 18,470 |
Municipal |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 6,145 |  | 6,874 |
Fair Value, Recurring [Member] | Level 1 |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 1,975 |  | 2,148 |
Equity securities, at fair value | 4,529 |  | 3,954 |
Short-term investments | 3,132 |  | 2,866 |
Other investments, at fair value | 417 |  | 434 | [1]
Securities lending collateral | 0 |  | 0 |
Investment derivative instruments, assets | 55 |  | 35 |
Other Derivative Instruments Fair Value | 10 |  |  |
Separate Account Asset | 5,014 |  | 4,264 |
Total assets measured at fair value | 15,132 | [2] | 13,701 | [1]
Investment derivative instruments, liabilities | 94 |  | 52 |
Other derivative instruments, liability | 12 |  | 17 |
Liabilities Related to Investment Contracts, Fair Value Disclosure | 106 |  | 69 |
Fair Value, Recurring [Member] | Level 1 | U.S. Treasury / Agency |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 1,975 |  | 2,148 |
Fair Value, Recurring [Member] | Level 1 | Non-U.S. |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 0 |  | 0 |
Fair Value, Recurring [Member] | Level 1 | Corporate and asset-backed securities |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 0 |  | 0 |
Fair Value, Recurring [Member] | Level 1 | Mortgage-backed securities |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 0 |  | 0 |
Fair Value, Recurring [Member] | Level 1 | Municipal |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 0 |  | 0 |
Fair Value, Recurring [Member] | Level 1 | GLB |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross | 0 |  | 0 | [3]
Fair Value, Recurring [Member] | Level 2 |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 87,811 |  | 86,372 |
Equity securities, at fair value | 0 |  | 0 |
Short-term investments | 1,335 |  | 1,474 |
Other investments, at fair value | 470 |  | 438 | [1]
Securities lending collateral | 2,369 |  | 1,844 |
Investment derivative instruments, assets | 0 |  | 0 |
Other Derivative Instruments Fair Value | 0 |  |  |
Separate Account Asset | 113 |  | 124 |
Total assets measured at fair value | 92,098 | [2] | 90,252 | [1]
Investment derivative instruments, liabilities | 0 |  | 0 |
Other derivative instruments, liability | 0 |  | 0 |
Liabilities Related to Investment Contracts, Fair Value Disclosure | 0 |  | 0 |
Fair Value, Recurring [Member] | Level 2 | U.S. Treasury / Agency |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 503 |  | 522 |
Fair Value, Recurring [Member] | Level 2 | Non-U.S. |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 25,770 |  | 25,808 |
Fair Value, Recurring [Member] | Level 2 | Corporate and asset-backed securities |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 35,887 |  | 34,758 |
Fair Value, Recurring [Member] | Level 2 | Mortgage-backed securities |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 19,506 |  | 18,410 |
Fair Value, Recurring [Member] | Level 2 | Municipal |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 6,145 |  | 6,874 |
Fair Value, Recurring [Member] | Level 2 | GLB |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross | 0 |  | 0 | [3]
Fair Value, Recurring [Member] | Level 3 |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 2,377 |  | 2,179 |
Equity securities, at fair value | 78 |  | 73 |
Short-term investments | 3 |  | 5 |
Other investments, at fair value | 10 |  | 10 | [1]
Securities lending collateral | 0 |  | 0 |
Investment derivative instruments, assets | 0 |  | 0 |
Other Derivative Instruments Fair Value | 0 |  |  |
Separate Account Asset | 0 |  | 0 |
Total assets measured at fair value | 2,468 | [2] | 2,267 | [1]
Investment derivative instruments, liabilities | 0 |  | 0 |
Other derivative instruments, liability | 0 |  | 0 |
Liabilities Related to Investment Contracts, Fair Value Disclosure | 760 |  | 1,089 |
Fair Value, Recurring [Member] | Level 3 | U.S. Treasury / Agency |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 0 |  | 0 |
Fair Value, Recurring [Member] | Level 3 | Non-U.S. |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 642 |  | 546 |
Fair Value, Recurring [Member] | Level 3 | Corporate and asset-backed securities |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 1,688 |  | 1,573 |
Fair Value, Recurring [Member] | Level 3 | Mortgage-backed securities |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 47 |  | 60 |
Fair Value, Recurring [Member] | Level 3 | Municipal |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 0 |  | 0 |
Fair Value, Recurring [Member] | Level 3 | GLB |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross | 760 |  | 1,089 | [3]
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 92,163 |  | 90,699 |
Equity securities, at fair value | 4,607 |  | 4,027 |
Short-term investments | 4,470 |  | 4,345 |
Other investments, at fair value | 897 |  | 882 | [1]
Securities lending collateral | 2,369 |  | 1,844 |
Investment derivative instruments, assets | 55 |  | 35 |
Other Derivative Instruments Fair Value | 10 |  |  |
Separate Account Asset | 5,127 |  | 4,388 |
Total assets measured at fair value | 109,698 | [2] | 106,220 | [1]
Investment derivative instruments, liabilities | 94 |  | 52 |
Other derivative instruments, liability | 12 |  | 17 |
Liabilities Related to Investment Contracts, Fair Value Disclosure | 866 |  | 1,158 |
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] | U.S. Treasury / Agency |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 2,478 |  | 2,670 |
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Non-U.S. |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 26,412 |  | 26,354 |
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Corporate and asset-backed securities |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 37,575 |  | 36,331 |
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Mortgage-backed securities |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 19,553 |  | 18,470 |
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Municipal |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Available for sale, Fair Value | 6,145 |  | 6,874 |
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] | GLB |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross | 760 |  | 1,089 | [3]
Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value [Member] |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Other investments, at fair value | 8,253 |  | 6,770 |
Policy Loans [Member] |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Other investments, at fair value | 237 |  | 233 |
Other Investments [Member] |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] |  |  |  |
Other investments, at fair value | $ 70 |  | $ 60 |
[1] | Excluded from the table above are partially-owned investments, investment funds, and limited partnerships of $6,770 million, policy loans of $233 million and other investments of $60 million at December 31, 2020 measured using NAV as a practical expedient.
[2] | Excluded from the table above are partially-owned investments, investment funds, and limited partnerships of $8,253 million, policy loans of $237 million and other investments of $70 million at June 30, 2021 measured using NAV as a practical expedient.
[3] | Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value.

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