Accumulated Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity Attributable to Parent	$ 5,590	$ 4,874
Accumulated Other Comprehensive Income (Loss), Net of Tax	(62)	7	$ (121)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	(71)	126
Amounts reclassified from accumulated other comprehensive income (loss)	(11)	2
Reclassification of certain tax effects to retained earnings	13
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(69)	128
Benefits Liability, Net of Tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity Attributable to Parent	27	43	29
Other comprehensive income (loss) before reclassifications	(14)	12
Amounts reclassified from accumulated other comprehensive income (loss)	(11)	2
Reclassification of certain tax effects to retained earnings	9
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(16)	14
Cumulative Foreign Currency Exchange
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity Attributable to Parent	(89)	(36)	$ (150)
Other comprehensive income (loss) before reclassifications	(57)	114
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Reclassification of certain tax effects to retained earnings	4
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	$ (53)	$ 114