Income Taxes (Schedule of Reconciliation of Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Balance at January 1,	$ 79	$ 88	$ 123
Additions based on tax positions related to the current year	71	13	17
Additions for tax positions of previous years	5	1	6
Reductions for tax positions of prior years	0	(7)	(42)
Reductions due to lapse of statute of limitations	(7)	(14)	(7)
Settlements	(4)	(2)	(1)
Other	1	0	(8)
Balance at December 31,	$ 145	$ 79	$ 88