Schedule VI (details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplementary Information Concerning Property-Casualty Insurance Operations
Deferred acquisition costs	$ 2,025	$ 1,923	$ 1,849
Claims and claim adjustment expense reserves	49,650	47,949	48,295
Discount from reserves for unpaid claims	1,102	1,083
Unearned premiums	12,915	12,329	11,971
Earned premiums	25,683	24,534	23,874
Net investment income	2,397	2,302	2,379
Amortization of deferred acquisition costs	4,166	3,985	3,885
Net written premiums	26,219	24,958	24,121
Property casualty [Member]
Supplementary Information Concerning Property-Casualty Insurance Operations
Deferred acquisition costs	2,025	1,923	1,849
Claims and claim adjustment expense reserves	49,633	47,929	48,272	$ 49,824
Discount from reserves for unpaid claims	1,102	1,083	1,066
Unearned premiums	12,915	12,329	11,971
Earned premiums	25,683	24,534	23,874
Net investment income	2,397	2,302	2,379
Claims and claim adjustment expenses incurred related to current year	17,846	15,675	14,471
Claims and claim adjustment expenses incurred related to prior year	(458)	(680)	(817)
Amortization of deferred acquisition costs	4,166	3,985	3,885
Paid claims and claim adjustment expenses	16,043	14,796	14,474
Net written premiums	$ 26,219	$ 24,958	$ 24,121