Income Taxes (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Income Tax Disclosure [Line Items]
Unrecognized tax benefits	$ 3,211	$ 2,932
Portion that, if recognized, would reduce tax expense and effective tax rate	2,469	2,209
Accrued interest on unrecognized tax benefits	602	579
Accrued penalties on unrecognized tax benefits	79	65
Lower Limit [Member]
Income Tax Disclosure [Line Items]
Portion that, if recognized, would reduce tax expense and effective tax rate	0	0
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months lower limit	0	0
Upper Limit [Member]
Income Tax Disclosure [Line Items]
Portion that, if recognized, would reduce tax expense and effective tax rate	350	150
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months upper limit	$ 400	$ 600