Fair Value Measurements - Additional Information (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	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt from Level 3 to Level 2	$ (177)	$ 642	$ (665)	$ 773
Transfer of credit derivatives from Level 3 to level 2				62
Deferred fees on commitments and standby letters of credit	43		43		44
Period for which carrying amount of property is reduced			Not less than once every 45 days
Long-term Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt from Level 3 to Level 2	132	435	607	521
Foreign exchange derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfer of derivatives from Level 3 to Level 2	$ 370		$ 370