Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Dec. 31, 2010	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Effective tax rate	25.00%		25.00%	55.00%
State income tax benefit			$ 12	$ 21
Reduction in the liability for unrecognized tax benefits	3		3
Time limits for tax audit closings, settlements and expiration of applicable statutes of limitations in various jurisdictions			12 months
Deferred tax assets expected to be realized			More than 50 percent
Increase in tax expense from repatriation of foreign earnings		372
Increase in tax expense from repatriation of foreign earnings					65	89
Reversal of valuation allowance	$ 600		$ 600