Summary Of Major Accounting Policies - Principles of Consolidation And Repurchases (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 12, 2014
Schedule of Equity Method Investments [Line Items]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased		10,000,000
Stock Repurchase Program, Total Number of Shares Repurchased To Date	2,000,000
Stock Repurchase Program, Total Shares Repurchased To Date, Amount	$ 100
Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Percentage	50.00%
Equity Method Investment, Ownership Interest Threshold For Consolidation, Percentage	20.00%
Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Interest Threshold For Consolidation, Percentage	50.00%