Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Liability for unrecognized tax benefits	$ 546		$ 546		$ 548
Unrecognized tax benefits, accrued interest	67		67		58
Unrecognized tax benefits that would impact effective tax rate	224		224		$ 205
Interest expense related to taxing authority examinations	4	$ 4	4	$ 8
Interest expense related to taxing authority examinations, net of tax	$ 2	2	$ 2	5
Provision for income taxes, reduction related primarily to resolutions for prior year examinations		$ 22		$ 22