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, 2017	Mar. 31, 2016
Analysis of changes in the liability for losses and loss adjustment expenses, net of reinsurance
Balance at beginning of year	$ 8,563	$ 8,127
Less reinsurance recoverables, net of allowance	2,302	2,201
Net liability at beginning of year	6,261	5,926
Liability for losses and loss adjustment expenses, period increase (decrease) [Abstract]
Provision for losses and LAE occurring in the current period	637	609
Net increase (decrease) in the provision for claims of prior years:
Net increase (decrease) in the provision for claims of prior years	(28)	(28)
Total losses and LAE incurred	609	581
Payments for losses and LAE of:
Current year	(84)	(80)
Prior years	(470)	(467)
Total payments	(554)	(547)
Foreign currency translation and other	8	11
Net liability at end of period	6,324	5,971
Add back reinsurance recoverables, net of allowance	2,297	2,137
Gross unpaid losses and LAE included in the balance sheet at end of period	$ 8,621	$ 8,108