Income Taxes, Change in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unrecognized Tax Benefits [Roll Forward]
Balance as of beginning of year	$ 897	$ 970	$ 941
Additions for tax positions related to the current year	5	19	23
Additions for tax positions related to prior years	9	30	28
Reductions for tax positions related to prior years	(20)	(101)	(19)
Reductions for tax positions related to the lapse of applicable statute of limitations	(44)	(14)	(1)
Settlements	0	(7)	(2)
Balance as of end of year	$ 847	$ 897	$ 970