Income Taxes - Additional Information (Detail) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) apportionment_issue	Jun. 30, 2014	Jun. 30, 2015 USD ($) apportionment_issue	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Income Tax Disclosure [Abstract]
Effective income tax rate	32.40%	32.60%	32.40%	29.50%
Income Taxes [Line Items]
Unrecognized tax benefits	$ 10		$ 10		$ 10
Unrecognized tax benefits that, if recognized, would impact the effective tax rate	$ 7		$ 7
State apportionment issues expected to be resolve during the next 12 months | apportionment_issue	2		2
Net cash payments (receipts) for income tax (refunds)			$ 90	$ 54
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