Business, Basis of Presentation and Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018 segment	Dec. 31, 2017 USD ($)	Aug. 04, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of segments	3	3
Spinoff
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common Stock Distribution by Parent				80.80%
Parent percentage | Spinoff
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common Stock Retained by Parent				19.20%
Other Liabilities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			$ 46
Deferred Income Tax [Domain]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			(22)
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			40
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			15
Retained Earnings | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			38
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			$ (64)