Income Taxes (Unrecognized Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Unrecognized Tax Benefits [Line Items]
Unrecognized tax benefits	$ 3,106	$ 2,932	$ 3,904
Portion that, if recognized, would reduce tax expense and effective tax rate	2,253	2,209
Accrued interest on unrecognized tax benefits	559	579
Accrued penalties on unrecognized tax benefits	101	65
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months lower limit	0	0
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months upper limit	400	600
Reconciliation of the beginning and ending amounts of unrecognized tax benefits
Balance at January 1	2,932	3,904
Additions for tax positions of current year	181	124
Reductions for tax positions of current year	(9)	(13)
Additions for tax positions of prior years	522	423
Reductions for tax positions of prior years	(377)	(1,471)
Settlements with tax authorities	(141)	(30)
Expiration on the statute of limitations	(2)	(5)
Balance at December 31	3,106	2,932	3,904
Interest on tax deficiencies	(20)	(254)	(86)
Income tax penalties	22	(8)	0
Lower Limit [Member]
Unrecognized Tax Benefits [Line Items]
Portion that, if recognized, would reduce tax expense and effective tax rate	0	0
Upper Limit [Member]
Unrecognized Tax Benefits [Line Items]
Portion that, if recognized, would reduce tax expense and effective tax rate	$ 350	$ 150