Long-duration insurance contracts - Summary of changes in discounted present values of expected future policy benefits and expected future net premiums (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at March 31	$ 17,734	$ 17,987
Periodic Payment Annuity [Member]
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Balance at beginning of year	10,276	11,212
Balance at beginning of year at original discount rate	11,757	11,681
Effect of actual versus expected experience	2	2
Change in benefits, net	(120)	(115)
Interest accrual	138	136
Foreign currency effect	49	2
Ending balance at original discount rate	11,826	11,706
Effect of changes in discount rate assumptions	(1,450)	(957)
Expected future policy benefits at March 31	10,376	10,749
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at March 31	10,376	10,749
Liabilities for future policy benefits at March 31, net of reinsurance recoverables	10,376	10,749
Life and Health [Member]
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Balance at beginning of year	43,784	52,665
Balance at beginning of year at original discount rate	55,170	65,871
Effect of cash flow assumption changes	(75)	(34)
Effect of actual versus expected experience	218	(12,870)
Change in benefits, net	(562)	(449)
Interest accrual	318	284
Foreign currency effect	263	(389)
Ending balance at original discount rate	55,332	52,413
Effect of changes in discount rate assumptions	(12,086)	(11,627)
Expected future policy benefits at March 31	43,246	40,786
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at beginning of year	39,294	46,916
Balance at beginning of year at original discount rate	49,500	58,731
Effect of cash flow assumption changes	(66)	(25)
Effect of actual versus expected experience	195	(11,278)
Change in premiums, net	(544)	(407)
Interest accrual	285	251
Foreign currency effect	234	(358)
Ending balance at original discount rate	49,604	46,914
Effect of changes in discount rate assumptions	(10,843)	(10,387)
Expected future net premiums at March 31	38,761	36,527
Balance at March 31	4,485	4,259
Reinsurance recoverables	(47)	(50)
Liabilities for future policy benefits at March 31, net of reinsurance recoverables	$ 4,438	$ 4,209