Income Taxes (Schedule of Reconciliation of the Total Amount of Unrecognized Tax Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefit, beginning of year	$ 18	$ 15	$ 16
Gross increases - tax positions in current period		4
Lapse of statute of limitations		(1)	(1)
Unrecognized tax benefit, end of year	$ 18	$ 18	$ 15