Reclassifications from Accumulated Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, December 31, 2017				$ (44)
Amounts reclassified from other comprehensive income (loss)				4
Net current-period other comprehensive income (loss)	$ 4	$ 1	$ 1	4	$ 2
Ending balance, September 30, 2018	(40)			(40)
Pension And Other Postretirement [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, December 31, 2017				(30)
Amounts reclassified from other comprehensive income (loss)				4
Net current-period other comprehensive income (loss)				4
Ending balance, September 30, 2018	(26)			(26)
Foreign Currency [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, December 31, 2017				(14)
Ending balance, September 30, 2018	$ (14)			$ (14)