Accumulated other comprehensive income (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 42,732	$ 44,025
Other comprehensive income, net before reclassifications	(3,199)	3,591
Reclassifications from accumulated other comprehensive income	(116)	(2,195)
Ending Balance	39,417	45,421
Unrealized appreciation of investments, net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	45,636	44,042
Other comprehensive income, net before reclassifications	(2,306)	3,378
Reclassifications from accumulated other comprehensive income	(127)	(2,242)
Ending Balance	43,203	45,178
Foreign currency translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(1,957)	(146)
Other comprehensive income, net before reclassifications	(787)	247
Reclassifications from accumulated other comprehensive income		47
Ending Balance	(2,744)	148
Prior service and actuarial gains/losses of defined benefit pension plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(1,039)	46
Other comprehensive income, net before reclassifications	(6)	(31)
Reclassifications from accumulated other comprehensive income	8	27
Ending Balance	(1,037)	42
Other AOCI transactions [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	92	83
Other comprehensive income, net before reclassifications	(100)	(3)
Reclassifications from accumulated other comprehensive income	3	(27)
Ending Balance	$ (5)	$ 53