Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Income Tax Disclosure [Abstract]
Total income tax expense (benefit), rate	25.80%	21.30%	26.60%
Combined federal and state statutory tax rate	37.20%
Federal net deferred tax asset	$ 111	$ 129	$ 78
State deferred tax liability	10	8	23
Deferred tax assets, valuation allowance	$ 3	$ 3	$ 0