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Stock-Based Compensation (Narrative) (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Mar. 21, 2019
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Stock-Based Compensation [Line Items]          
Stock-based compensation expense   $ 2 $ 1 $ 7 $ 3
Stock-based compensation expense, net of tax   2 $ 1 5 $ 2
Total unrecognized compensation costs related to non-vested stock options, restricted share units and performance shares   $ 20   $ 20  
Weighted-average period of recognition of stock-based compensation cost       2 years 8 months 19 days  
Employee Stock Purchase Plan [Member]          
Stock-Based Compensation [Line Items]          
Maximum Percentage Of Current Fair Market Value Eligible Employees May Purchase 15.00%        
Number of shares of common stock authorized 1,250,000