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, 2021	Mar. 31, 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	726	749
Net increase (decrease) in the provision for claims of prior years	(59)	(42)
Total losses and LAE incurred	667	707
Payments for losses and LAE of:
Current year	(52)	(75)
Prior years	(622)	(676)
Total payments	(674)	(751)
Foreign currency translation and other	0	(22)
Net liability at end of period	7,268	7,142
Add back reinsurance recoverables, net of allowance	3,116	2,964
Gross unpaid losses and LAE included in the balance sheet at end of period	$ 10,384	$ 10,106