Income Taxes - Additional Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Unrecognized tax benefit, affect the effective tax rate	$ 329	$ 319
Accruals for payment of interest and penalties associated with uncertain tax positions	169	159
Increase in accruals for payment of interest and penalties associated with uncertain tax positions	10
Net deferred tax is a combination of deferred tax liabilities and valuation allwance	967	905
Tax Reserve	265
Accrued interest expenses to recognize the estimated tax exposure	$ 139