Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Liability for unrecognized tax benefits	$ 503		$ 503		$ 462
Unrecognized tax benefits, accrued interest	43		43		30
Unrecognized tax benefits that would impact effective tax rate	180		180		160
Interest expense related to taxing authority examinations	3	7
Reductions in interest expense related to taxing authority examinations			11	8
Interest expense related to taxing authority examinations, net of tax	2	4
Reductions in interest expense related to taxing authority examinations, net of tax			$ 7	$ 5