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, 2011	Dec. 31, 2010	Dec. 31, 2009
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	$ 60,075	$ 59,416	$ 56,620
Ceded losses and deferred charges at beginning of year	(6,545)	(6,879)	(7,133)
Net balance at beginning of year	53,530	52,537	49,487
Incurred losses recorded during the year for the current accident year	23,031	20,357	19,156
Incurred losses recorded during the current year for prior accident years	(2,202)	(2,270)	(905)
Total incurred losses	20,829	18,087	18,251
Payments during the year with respect to the current accident year	(9,269)	(7,666)	(7,207)
Payments during the year with respect to prior accident years	(8,854)	(9,191)	(8,315)
Total payments	(18,123)	(16,857)	(15,522)
Net balance at end of year	56,236	53,767	52,216
Ceded losses and deferred charges at end of year	7,092	6,545	6,879
Foreign currency translation adjustment	(100)	(312)	232
Acquisitions	591	75	89
Gross liabilities at end of year	$ 63,819	$ 60,075	$ 59,416