Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Line Items]
Unrecognized tax benefits	$ 3,310	$ 3,223
Portion that, if recognized, would reduce tax expense and effective tax rate	2,360	2,346
Accrued interest on unrecognized tax benefits	558	570
Accrued penalties on unrecognized tax benefits	100	97
Lower Limit [Member]
Income Tax Disclosure [Line Items]
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months lower limit	0	0
Portion that, if recognized, would reduce tax expense and effective tax rate	0	0
Upper Limit [Member]
Income Tax Disclosure [Line Items]
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months upper limit	1,000	800
Portion that, if recognized, would reduce tax expense and effective tax rate	$ 260	$ 250