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	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at January 1	$ 20,213	$ 19,753	$ 27,295
Periodic Payment Annuities [Member]
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Balance at beginning of year	10,640	16,153	17,122
Balance at beginning of year at original discount rate	11,549	11,261	10,569
Effect of actual from expected experience	5	121	8
Change in benefits, net	(470)	(297)	138
Interest accrual	537	535	528
Foreign currency effect	60	(71)	18
Ending balance at original discount rate	11,681	11,549	11,261
Effect of changes in discount rate assumptions	(469)	(909)	4,892
Expected future policy benefits at December 31	11,212	10,640	16,153
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at January 1	11,212	10,640	16,153
Liability for future policy benefits at December 31, net of reinsurance recoverables	11,212	10,640	16,153
Life and Health [Member]
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Balance at beginning of year	52,008	63,648	66,528
Balance at beginning of year at original discount rate	63,584	60,133	58,247
Effect of cash flow assumption changes	(829)	2,261	(354)
Effect of actual from expected experience	(352)	927	1,011
Change in benefits, net	1,616	671	394
Interest accrual	1,787	1,644	1,670
Foreign currency effect	65	(2,052)	(835)
Ending balance at original discount rate	65,871	63,584	60,133
Effect of changes in discount rate assumptions	(13,206)	(11,576)	3,515
Expected future policy benefits at December 31	52,665	52,008	63,648
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at beginning of year	46,129	55,960	58,198
Balance at beginning of year at original discount rate	56,535	53,277	51,370
Effect of cash flow assumption changes	(880)	2,163	(270)
Effect of actual from expected experience	(181)	676	572
Change in premiums, net	1,645	928	908
Interest accrual	1,566	1,434	1,444
Foreign currency effect	46	(1,943)	(747)
Ending balance at original discount rate	58,731	56,535	53,277
Effect of changes in discount rate assumptions	(11,815)	(10,406)	2,683
Expected future net premiums at December 31	46,916	46,129	55,960
Balance at January 1	5,749	5,879	7,688
Reinsurance recoverables	(1,571)	(1,559)	(2,152)
Liability for future policy benefits at December 31, net of reinsurance recoverables	$ 4,178	$ 4,320	$ 5,536