Income Taxes, Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unrecognized Tax Benefits [Roll Forward]
Balance as of beginning of year	$ 941	$ 936	$ 964
Additions based on tax positions related to the current year	23	33	36
Additions for tax positions related to prior years	28	15	11
Reductions for tax positions related to prior years	(19)	(42)	(46)
Reductions for tax positions related to the lapse of applicable statute of limitations	(1)	(1)	(3)
Settlements	(2)	0	(237)
Reclassification of uncertain tax receivable to long-term receivable from IRS	0	0	211
Balance as of end of year	$ 970	$ 941	$ 936