Income Taxes, Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Unrecognized Tax Benefits [Roll Forward]
Balance as of beginning of year	$ 970	$ 941	$ 936
Additions for tax positions related to the current year	19	23	33
Additions for tax positions related to prior years	30	28	15
Reductions for tax positions related to prior years	(101)	(19)	(42)
Reductions for tax positions related to the lapse of applicable statute of limitations	(14)	(1)	(1)
Settlements	(7)	(2)	0
Balance as of end of year	$ 897	$ 970	$ 941