Income Taxes- Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Jun. 30, 2013
Income Tax Disclosure [Abstract]
Tax Litigation Redetermination	$ 261
Tax reserves	840	840		1,060
Impact on tax expense if tax reserves were unnecessary		840
Accrued interest, related to income taxes in the balance sheet	198	198
Additional tax expense related to interest		187	10
Reasonably possible decrease in uncertain tax positions within the next 12 months, if a re-evaluation is required	$ 72	$ 72