Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Net income tax payments/(refunds)	$ 1,326	$ 896	$ 1,460
Unrecognized tax benefits that would affect the effective tax rate, if recognized	1,405	1,568	1,402
Unrecognized tax benefits	2,412	$ 1,736	$ 1,557	$ 1,617
State and Local Jurisdiction [Member]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ (460)