Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Liability for unrecognized tax benefits	$ 541		$ 541		$ 548
Unrecognized tax benefits, accrued interest	69		69		58
Unrecognized tax benefits that would impact effective tax rate	228		228		$ 205
Interest expense related to taxing authority examinations	2	$ 3	6	$ 11
Interest expense related to taxing authority examinations, net of tax	$ 1	$ 2	$ 4	$ 7