Unpaid losses and loss adjustment expenses (Detail) (Property, Liability and Casualty Unpaid Losses and Loss Adjustment Expense Reserves [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, Liability and Casualty Unpaid Losses and Loss Adjustment Expense Reserves [Member]
Unpaid Losses and Loss Adjustment Expenses [Line Items]
Gross liabilities at beginning of year	$ 64,160	$ 63,819	$ 60,075
Ceded losses and deferred charges at beginning of year	(6,944)	(7,092)	(6,545)
Net balance at beginning of year	57,216	56,727	53,530
Incurred losses recorded during the year for the current accident year	23,027	22,239	23,031
Incurred losses recorded during the current year for prior accident years	(1,752)	(2,126)	(2,202)
Total incurred losses	21,275	20,113	20,829
Payments during the year with respect to the current accident year	(10,154)	(9,667)	(9,269)
Payments during the year with respect to prior accident years	(10,978)	(10,628)	(8,854)
Total payments	(21,132)	(20,295)	(18,123)
Net balance at end of year	57,359	56,545	56,236
Ceded losses and deferred charges at end of year	7,414	6,944	7,092
Foreign currency translation adjustment	93	186	(100)
Business acquisitions		485	591
Gross liabilities at end of year	$ 64,866	$ 64,160	$ 63,819