Description of Business, Basis of Presentation, and Significant Accounting Policies Description of Business, Basis of Presentation, and Significant Accounting Policies (Recently Issued Accounting Standards) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Accounting Standards Update 2014-09 [Member]
Accounting Standards Update [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 126
Accounting Standards Update 2016-01 [Member]
Accounting Standards Update [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 20