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	$ 5,911	$ 5,816
Portion that, if recognized, would reduce tax expense and effective tax rate	4,223	4,307
Accrued interest on unrecognized tax benefits	970	975
Accrued penalties on unrecognized tax benefits	169	164
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	1,150	900
Portion that, if recognized, would reduce tax expense and effective tax rate	$ 400	$ 350