Accumulated other comprehensive income (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 286,359	$ 258,627
Ending Balance	304,093	266,258
Unrealized appreciation of investments, net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	43,176	38,598
Other comprehensive income, net before reclassifications	8,540	(1,971)
Reclassifications from accumulated other comprehensive income into net earnings	(383)	(1,180)
Ending Balance	51,333	35,447
Foreign currency translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(5,268)	(3,856)
Other comprehensive income, net before reclassifications	1,221	(78)
Ending Balance	(4,047)	(3,934)
Prior service and actuarial gains/losses of defined benefit pension plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(593)	(762)
Other comprehensive income, net before reclassifications	(64)	(5)
Reclassifications from accumulated other comprehensive income into net earnings	34	35
Ending Balance	(623)	(732)
Other AOCI transactions [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(17)	2
Other comprehensive income, net before reclassifications	(7)	(22)
Reclassifications from accumulated other comprehensive income into net earnings	13	16
Ending Balance	(11)	(4)
Accumulated other comprehensive income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	37,298	33,982
Other comprehensive income, net before reclassifications	9,690	(2,076)
Reclassifications from accumulated other comprehensive income into net earnings	(336)	(1,129)
Ending Balance	$ 46,652	$ 30,777