Income Tax (Reconciliation of Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits
Balance at January 1,	$ 1,102	$ 1,146	$ 1,259
Additions for tax positions of prior years (1)	269	70	24
Reductions for tax positions of prior years (2)	(195)	(101)	(112)
Additions for tax positions of current year (1)	226	33	23
Reductions for tax positions of current year	(3)	(3)	0
Settlements with tax authorities (3)	(288)	(43)	(48)
Balance at December 31,	1,111	1,102	1,146
Unrecognized tax benefits that, if recognized, would impact the effective rate	1,046	$ 1,073	$ 1,112
Current Income Tax Payable
Reconciliation of Unrecognized Tax Benefits
Settlements with tax authorities (3)	$ (284)