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Investments in fixed maturity securities (Detail) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Summary of Investment Holdings [Line Items] |  |
Amortized cost of fixed maturity securities | $ 15,214 | $ 23,525
Unrealized gains on fixed maturity securities | 257 | 334
Unrealized losses on fixed maturity securities | (107) | (101)
Fair value of fixed maturity securities | 15,364 | 23,758
U.S. Treasury, U.S. government corporations and agencies [Member] |  |
Summary of Investment Holdings [Line Items] |  |
Amortized cost of fixed maturity securities | 4,447 | 10,308
Unrealized gains on fixed maturity securities | 16 | 14
Unrealized losses on fixed maturity securities | (4) | (53)
Fair value of fixed maturity securities | 4,459 | 10,269
Foreign governments [Member] |  |
Summary of Investment Holdings [Line Items] |  |
Amortized cost of fixed maturity securities | 9,443 | 11,788
Unrealized gains on fixed maturity securities | 16 | 58
Unrealized losses on fixed maturity securities | (97) | (41)
Fair value of fixed maturity securities | 9,362 | 11,805
Corporate and Other [Member] |  |
Summary of Investment Holdings [Line Items] |  |
Amortized cost of fixed maturity securities | 1,324 | 1,429
Unrealized gains on fixed maturity securities | 225 | 262
Unrealized losses on fixed maturity securities | (6) | (7)
Fair value of fixed maturity securities | $ 1,543 | $ 1,684

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