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, 2023	Sep. 30, 2022
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Liability for future policy benefits at September 30	$ 18,556	$ 18,913
Periodic Payment Annuities [Member]
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Balance at beginning of period	10,640	16,153
Balance at beginning of period at original discount rate	11,549	11,261
Effect of actual from expected results	3	126
Change in benefits, net	(349)	(235)
Interest accrual	402	404
Foreign currency effect	27	(127)
Ending balance at original discount rate	11,632	11,429
Effect of changes in discount rate assumptions	(1,692)	(1,320)
Expected future policy benefits at September 30	9,940	10,109
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Liability for future policy benefits at September 30	9,940	10,109
Liability for future policy benefits at September 30, net of reinsurance recoverables	9,940	10,109
Life and Health [Member]
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Balance at beginning of period	52,008	63,648
Balance at beginning of period at original discount rate	63,584	60,133
Effect of cash flow assumption changes	346	1,342
Effect of actual from expected results	(425)	742
Change in benefits, net	(2,059)	(2,022)
Interest accrual	1,288	1,221
Foreign currency effect	(528)	(2,887)
Ending balance at original discount rate	62,206	58,529
Effect of changes in discount rate assumptions	(13,434)	(11,400)
Expected future policy benefits at September 30	48,772	47,129
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at beginning of period	46,129	55,960
Balance at beginning of period at original discount rate	56,535	53,277
Effect of cash flow assumption changes	276	1,333
Effect of actual from expected results	(266)	472
Change in premiums, net	(1,833)	(1,609)
Interest accrual	1,125	1,062
Foreign currency effect	(502)	(2,717)
Ending balance at original discount rate	55,335	51,818
Effect of changes in discount rate assumptions	(11,928)	(10,163)
Expected future net premiums at September 30	43,407	41,655
Liability for future policy benefits at September 30	5,365	5,474
Reinsurance recoverables	(1,399)	(1,493)
Liability for future policy benefits at September 30, net of reinsurance recoverables	$ 3,966	$ 3,981