Insurance - Analysis of changes in the liability for losses and loss adjustment expenses, net of reinsurance (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 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	2,543	2,560
Net increase (decrease) in the provision for claims of prior years	(208)	(166)
Total losses and LAE incurred	2,335	2,441
Payments for losses and LAE of:
Current year	(589)	(592)
Prior years	(1,430)	(1,406)
Total payments	(2,019)	(1,998)
Foreign currency translation and other	0	(11)
Net liability at end of period	7,591	7,640
Add back reinsurance recoverables, net of allowance	3,400	3,114
Gross unpaid losses and LAE included in the balance sheet at end of period	10,991	10,754
Property and Casualty Insurance | Other lines
Liability for losses and loss adjustment expenses, period increase (decrease) [Abstract]
Special A&E charges	$ 0	$ 47