Income Taxes (Unrecognized Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Line Items]
Unrecognized tax benefits	$ 2,961	$ 3,055
Portion that, if recognized, would reduce tax expense and effective tax rate	2,245	2,259
Accrued interest on unrecognized tax benefits	417	420
Accrued penalties on unrecognized tax benefits	33	34
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	600	600
Minimum [Member]
Income Tax Disclosure [Line Items]
Portion that, if recognized, would reduce tax expense and effective tax rate	0	0
Maximum [Member]
Income Tax Disclosure [Line Items]
Portion that, if recognized, would reduce tax expense and effective tax rate	$ 50	$ (50)