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, 2024	Dec. 31, 2023
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at December 31	$ 17,616	$ 20,213
Annuities [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 from expected experience	3	5
Change in benefits, net	(478)	(470)
Interest accrual	550	537
Foreign currency effect	1	60
Ending balance at original discount rate	11,757	11,681
Effect of changes in discount rate assumptions	(1,481)	(469)
Expected future policy benefits at December 31	10,276	11,212
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Balance at December 31	10,276	11,212
Liability for future policy benefits at December 31, net of reinsurance recoverables	10,276	11,212
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	(348)	(829)
Effect of actual from expected experience	(12,711)	(352)
Change in benefits, net	1,991	1,616
Interest accrual	1,234	1,787
Foreign currency effect	(867)	65
Ending balance at original discount rate	55,170	65,871
Effect of changes in discount rate assumptions	(11,386)	(13,206)
Expected future policy benefits at December 31	43,784	52,665
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	(416)	(880)
Effect of actual from expected experience	(11,104)	(181)
Change in premiums, net	1,984	1,645
Interest accrual	1,099	1,566
Foreign currency effect	(794)	46
Ending balance at original discount rate	49,500	58,731
Effect of changes in discount rate assumptions	(10,206)	(11,815)
Expected future net premiums at December 31	39,294	46,916
Balance at December 31	4,490	5,749
Reinsurance recoverables	(46)	(1,571)
Liability for future policy benefits at December 31, net of reinsurance recoverables	$ 4,444	$ 4,178