Income Taxes (Balance of unrecognized tax benefits) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Income Tax Disclosure [Line Items]
Unrecognized tax benefits	$ 6,572		$ 6,572		$ 6,778
Portion that, if recognized, would reduce tax expense and effective tax rate	4,164		4,164		4,723
Accrued interest on unrecognized tax benefits	945		945		805
Accrued penalties on unrecognized tax benefits	135		135		98
Benefit (provision) for income taxes	(479)	$ (799)	(340)	$ (7,093)
Lower Limit
Income Tax Disclosure [Line Items]
Portion that, if recognized, would reduce tax expense and effective tax rate	0		0		0
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months lower limit	0		0		0
Upper Limit
Income Tax Disclosure [Line Items]
Portion that, if recognized, would reduce tax expense and effective tax rate	800		800		200
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months lower limit	$ 1,400		$ 1,400		$ 700