Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Liability for unrecognized tax benefits	$ 417		$ 417		$ 426
Unrecognized tax benefits, accrued interest	26		26		14
Unrecognized tax benefits that would impact effective tax rate	151		151		125
Reductions in interest related to taxing authority examinations	7	1	(8)	(20)
Reductions in interest related to taxing authority examinations net of tax	$ 4	$ 0	$ (5)	$ (13)