Reclassifications from Accumulated Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, December 31, 2016	$ (39)
Other comprehensive income (loss) before reclassifications	(7)
Amounts reclassified from other comprehensive income (loss)	2
Net current-period other comprehensive income (loss)	(5)	$ 9	$ (110)
Ending balance, December 31, 2017	(44)	(39)
Pension And Other Postretirement [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, December 31, 2016	(19)
Other comprehensive income (loss) before reclassifications	(13)
Amounts reclassified from other comprehensive income (loss)	2
Net current-period other comprehensive income (loss)	(11)
Ending balance, December 31, 2017	(30)	(19)
Foreign Currency [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, December 31, 2016	(20)
Other comprehensive income (loss) before reclassifications	6
Net current-period other comprehensive income (loss)	6
Ending balance, December 31, 2017	$ (14)	$ (20)