Income Taxes - Additional Information (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Unrecognized tax benefit, affect the effective tax rate	$ 334	$ 314	$ 276
Accruals for payment of interest and penalties associated with uncertain tax positions	208	159	130
Increase in accruals for payment of interest and penalties associated with uncertain tax positions	49	29
Net deferred tax asset	$ 1,557	$ 905