Insurance - Analysis of changes in the liability for losses and loss adjustment expenses, net of reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Analysis of changes in the liability for losses and loss adjustment expenses, net of reinsurance
Balance at beginning of period	$ 14,179	$ 13,087	$ 11,974	$ 11,074
Less reinsurance recoverables, net of allowance	4,957	4,288	3,767	3,419
Net liability at beginning of period	8,799	8,207	7,655
Provision for losses and LAE occurring in the current year	4,524	4,256	3,914
Net increase (decrease) in the provision for claims of prior years:
Total losses and LAE incurred	4,460	4,033	3,629
Payments for losses and LAE of:
Current year	(1,497)	(1,261)	(1,212)
Prior years	(2,537)	(2,181)	(1,870)
Total payments	(4,034)	(3,442)	(3,082)
Foreign currency translation and other	(3)	1	5
Net liability at end of period	9,222	8,799	8,207
Add back reinsurance recoverables, net of allowance	4,957	4,288	3,767
Unpaid losses and loss adjustment expenses	14,179	13,087	11,974	$ 11,074
Net decrease in the provision for claims of prior years
Net increase (decrease) in the provision for claims of prior years:
Prior year claims and claims adjustment expense	$ (64)	$ (223)	$ (285)