Insurance - Analysis of changes in the liability for losses and loss adjustment expenses, net of reinsurance (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Analysis of changes in the liability for losses and loss adjustment expenses, net of reinsurance
Balance at beginning of year	$ 14,179	$ 13,087
Less reinsurance recoverables, net of allowance	4,957	4,288
Net liability at beginning of year	9,222	8,799
Provision for losses and LAE occurring in the current period	985	962
Net decrease in the provision for claims of prior years	(20)	(50)
Total losses and LAE incurred	965	912
Payments for losses and LAE of:
Current year	(104)	(94)
Prior years	(863)	(895)
Total payments	(967)	(989)
Foreign currency translation and other	(2)	1
Net liability at end of period	9,218	8,723
Add back reinsurance recoverables, net of allowance	4,752	4,327
Gross unpaid losses and LAE included in the balance sheet at end of period	$ 13,970	$ 13,050