Income Tax (Reconciliation of Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits
Balance at January 1,	$ 256	$ 1,111	$ 1,102
Additions for tax positions of prior years (1)	16	6	269
Reductions for tax positions of prior years (2)	(1)	(493)	(195)
Additions for tax positions of current year (1)	12	13	226
Reductions for tax positions of current year	0	0	(3)
Settlements with tax authorities (3)	(1)	(381)	(288)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	(10)	0	0
Balance at December 31,	272	256	1,111
Unrecognized tax benefits that, if recognized, would impact the effective rate	$ 203	194	1,046
Current Income Tax Payable
Reconciliation of Unrecognized Tax Benefits
Settlements with tax authorities (3)		$ (377)	$ (284)