Income Taxes (Balance of unrecognized tax benefits) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Income Tax Disclosure [Line Items]
Unrecognized tax benefits	$ 4,732		$ 4,692
Portion that, if recognized, would reduce tax expense and effective tax rate	2,872		2,886
Accrued interest on unrecognized tax benefits	645		615
Accrued penalties on unrecognized tax benefits	119		118
Benefit (provision) for income taxes	(16)	$ 177
Lower Limit
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
Income Tax Disclosure [Line Items]
Portion that, if recognized, would reduce tax expense and effective tax rate	500		500
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months lower limit	$ 600		$ 600