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, 2012	Dec. 31, 2011	Dec. 31, 2010
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	$ 63,819	$ 60,075	$ 59,416
Ceded losses and deferred charges at beginning of year	(7,092)	(6,545)	(6,879)
Net balance at beginning of year	56,727	53,530	52,537
Incurred losses recorded during the year for the current accident year	22,239	23,031	20,357
Incurred losses recorded during the current year for prior accident years	(2,126)	(2,202)	(2,270)
Total incurred losses	20,113	20,829	18,087
Payments during the year with respect to the current accident year	(9,667)	(9,269)	(7,666)
Payments during the year with respect to prior accident years	(10,628)	(8,854)	(9,191)
Total payments	(20,295)	(18,123)	(16,857)
Net balance at end of year	56,545	56,236	53,767
Ceded losses and deferred charges at end of year	6,944	7,092	6,545
Foreign currency translation adjustment	186	(100)	(312)
Business acquisitions	485	591	75
Gross liabilities at end of year	$ 64,160	$ 63,819	$ 60,075