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, 2024	Mar. 31, 2023
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at March 31	$ 17,987	$ 19,937
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	1
Change in benefits, net	(115)	(116)
Interest accrual	136	133
Foreign currency effect	2	19
Ending balance at original discount rate	11,706	11,586
Effect of changes in discount rate assumptions	(957)	(412)
Expected future policy benefits at March 31	10,749	11,174
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at March 31	10,749	11,174
Liabilities for future policy benefits at March 31, net of reinsurance recoverables	10,749	11,174
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	(34)	(1)
Effect of actual versus expected experience	(12,870)	(519)
Change in benefits, net	(449)	(747)
Interest accrual	284	425
Foreign currency effect	(389)	47
Ending balance at original discount rate	52,413	62,789
Effect of changes in discount rate assumptions	(11,627)	(12,169)
Expected future policy benefits at March 31	40,786	50,620
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	(25)	2
Effect of actual versus expected experience	(11,278)	(413)
Change in premiums, net	(407)	(660)
Interest accrual	251	371
Foreign currency effect	(358)	47
Ending balance at original discount rate	46,914	55,882
Effect of changes in discount rate assumptions	(10,387)	(10,895)
Expected future net premiums at March 31	36,527	44,987
Balance at March 31	4,259	5,633
Reinsurance recoverables	(50)	(1,565)
Liabilities for future policy benefits at March 31, net of reinsurance recoverables	$ 4,209	$ 4,068