Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Total income tax expense (benefit), rate	27.80%	25.80%
Combined federal and state statutory tax rate	37.20%
Federal net deferred tax asset	$ 148	$ 111	$ 201
State deferred tax asset	4	10	9
Deferred tax assets, valuation allowance	1	3	1
Reduction in federal tax credit carryforward	$ 1