Insurance - Analysis of changes in the liability for losses and loss adjustment expenses, net of reinsurance (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Analysis of changes in the liability for losses and loss adjustment expenses, net of reinsurance
Balance at beginning of year	$ 10,392	$ 10,232
Less reinsurance recoverables, net of allowance	3,117	3,024
Net liability at beginning of year	7,275	7,208
Liability for losses and loss adjustment expenses, period increase (decrease) [Abstract]
Provision for losses and LAE occurring in the current period	1,507	1,597
Net increase (decrease) in the provision for claims of prior years	(126)	(119)
Total losses and LAE incurred	1,381	1,478
Payments for losses and LAE of:
Current year	(258)	(284)
Prior years	(1,083)	(1,068)
Total payments	(1,341)	(1,352)
Foreign currency translation and other	1	(20)
Net liability at end of period	7,316	7,314
Add back reinsurance recoverables, net of allowance	3,182	3,007
Gross unpaid losses and LAE included in the balance sheet at end of period	$ 10,498	$ 10,321