Unpaid losses and loss expenses Unpaid losses and loss expenses (RF Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Jan. 14, 2016
Unpaid Losses and Loss Expenses [Roll Forward]
Gross unpaid losses and loss expenses, beginning of year	$ 60,540	$ 37,303
Reinsurance Recoverable on unpaid losses, beginning of year	(12,708)	(10,741)
Net unpaid loss, beginning of period	47,832	26,562
Acquisition of subsidiaries			$ 0	$ 21,398
Total, Beginning of year	47,832	47,960
Current Year Claims and Claims Adjustment Expense	8,396	8,529
PPD (Favorable) / Adverse	(461)	(601)
Total, Incurred	7,935	7,928
Net loss and loss expenses paid, Current Year	2,271	1,964
Net losses and loss expenses Paid, Prior Years	5,758	5,541
Total, Paid	8,029	7,505
Liability For Unpaid Claims And Claims Adjustment Expense Foreign Currency Revaluation And Other	171	40
Net unpaid Loss, end of period	47,909	48,423
Reinsurance Recoverables on unpaid losses, end of year	12,485	12,396
Gross unpaid losses and loss expenses, end of year	60,394	60,819
prior period development, net adjustments	$ 60	$ 53