Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Jun. 30, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Total income tax expense (benefit), rate	26.70%	25.80%	19.20%
Combined federal and state statutory tax rate				37.20%
Federal net deferred tax asset	$ 197		$ 111	$ 197	$ 129
State deferred tax liability			22		8
State deferred tax asset	1			1
Deferred tax assets, valuation allowance	$ 2		$ 0	$ 2	$ 3