Income Taxes - Additional Information (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) apportionment_issue	Sep. 30, 2014	Sep. 30, 2015 USD ($) apportionment_issue	Sep. 30, 2014 USD ($)
Income Tax Disclosure [Abstract]
Effective income tax rate	32.40%	33.90%	32.40%	31.00%
Income Taxes [Line Items]
Unrecognized tax benefits	$ 29		$ 29
Unrecognized tax benefits, increased by current period tax positions	19
Unrecognized tax benefits that, if recognized, would impact the effective tax rate	$ 21		$ 21
Number of state apportionment issues during the next 12 months | apportionment_issue	2		2
Number of issues under audit | apportionment_issue	1,000,000		1,000,000
Number of issues pending an expected court ruling | apportionment_issue	1,000,000		1,000,000
Net cash payments for income taxes, net of refunds			$ 161	$ 105
US Federal Tax Issue
Income Taxes [Line Items]
Change in unrecognized tax benefits, amount of unrecorded benefit	$ 21		21
State Apportionment Issues
Income Taxes [Line Items]
Change in unrecognized tax benefits, amount of unrecorded benefit	$ 4		$ 4