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	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at September 30	$ 18,612	$ 18,556
Periodic Payment Annuity [Member]
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Balance at beginning of year	11,212	10,640
Balance at beginning of year at original discount rate	11,681	11,549
Effect of actual versus expected experience	2	3
Change in benefits, net	(357)	(349)
Interest accrual	411	402
Foreign currency effect	96	27
Ending balance at original discount rate	11,833	11,632
Effect of changes in discount rate assumptions	(697)	(1,692)
Expected future policy benefits at September 30	11,136	9,940
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at September 30	11,136	9,940
Liabilities for future policy benefits at September 30, net of reinsurance recoverables	11,136	9,940
Life and Health [Member]
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Balance at beginning of year	52,665	52,008
Balance at beginning of year at original discount rate	65,871	63,584
Effect of cash flow assumption changes	1,485	346
Effect of actual versus expected experience	(12,709)	(425)
Change in benefits, net	(1,404)	(2,059)
Interest accrual	891	1,288
Foreign currency effect	218	(528)
Ending balance at original discount rate	54,352	62,206
Effect of changes in discount rate assumptions	(11,111)	(13,434)
Expected future policy benefits at September 30	43,241	48,772
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at beginning of year	46,916	46,129
Balance at beginning of year at original discount rate	58,731	56,535
Effect of cash flow assumption changes	1,449	276
Effect of actual versus expected experience	(11,033)	(266)
Change in premiums, net	(1,348)	(1,833)
Interest accrual	791	1,125
Foreign currency effect	200	(502)
Ending balance at original discount rate	48,790	55,335
Effect of changes in discount rate assumptions	(10,005)	(11,928)
Expected future net premiums at September 30	38,785	43,407
Balance at September 30	4,456	5,365
Reinsurance recoverables	(52)	(1,399)
Liabilities for future policy benefits at September 30, net of reinsurance recoverables	$ 4,404	$ 3,966