Fixed Assets - Depreciation Expense Relating to Fixed Assets (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Property, Plant and Equipment [Line Items]
Depreciation expense relating to fixed assets	$ 730	$ 687	$ 2,144	$ 2,014