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
Income Taxes
Provision for income tax	$ 108	$ 167	$ 232	$ 287
Effective tax rate	26.10%	27.60%	25.80%	27.50%