Investments in fixed maturity securities (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 21,485	$ 15,964
Unrealized gains on fixed maturity securities	396	510
Unrealized losses on fixed maturity securities	(163)	(40)
Fair value of fixed maturity securities	21,718	16,434
U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	8,793	3,286
Unrealized gains on fixed maturity securities	12	22
Unrealized losses on fixed maturity securities	(97)	(5)
Fair value of fixed maturity securities	8,708	3,303
Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	11,116	10,998
Unrealized gains on fixed maturity securities	26	29
Unrealized losses on fixed maturity securities	(62)	(33)
Fair value of fixed maturity securities	11,080	10,994
Corporate bonds [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	1,268	1,363
Unrealized gains on fixed maturity securities	324	412
Unrealized losses on fixed maturity securities	(2)	(1)
Fair value of fixed maturity securities	1,590	1,774
Other [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	308	317
Unrealized gains on fixed maturity securities	34	47
Unrealized losses on fixed maturity securities	(2)	(1)
Fair value of fixed maturity securities	$ 340	$ 363

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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