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Investments in fixed maturity securities (Detail) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 17,675	$ 15,214
Unrealized gains on fixed maturity securities	291	257
Unrealized losses on fixed maturity securities	(23)	(107)
Fair value of fixed maturity securities	17,943	15,364
U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	4,613	4,447
Unrealized gains on fixed maturity securities	13	16
Unrealized losses on fixed maturity securities	0	(4)
Fair value of fixed maturity securities	4,626	4,459
Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	11,822	9,443
Unrealized gains on fixed maturity securities	39	16
Unrealized losses on fixed maturity securities	(19)	(97)
Fair value of fixed maturity securities	11,842	9,362
Corporate and Other [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	1,240	1,324
Unrealized gains on fixed maturity securities	239	225
Unrealized losses on fixed maturity securities	(4)	(6)
Fair value of fixed maturity securities	$ 1,475	$ 1,543

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