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Stock-Based Compensation (Narrative) (Details) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended 9 Months Ended
Feb. 24, 2015
Feb. 28, 2019
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Nov. 03, 2015
Apr. 27, 2015
Stock-Based Compensation [Line Items]                
Stock-based compensation expense     $ 3 $ 3 $ 13 $ 10    
Stock-based compensation expense, net of tax     3 $ 2 9 $ 8    
Total unrecognized compensation costs related to non-vested stock options and restricted share units     $ 39   $ 39      
Weighted-average period of recognition of stock-based compensation cost         1 year 11 months 12 days      
Percent of current fair market value, discount eligible employees may purchase common stock   10.00%            
Employee Stock Purchase Plan, maximum number of shares of common stock authorized for sale             1,000,000  
Employee stock plan, shares remaining in ESPP   843,584            
Number of shares of available for issuance     790,543   790,543      
Expiration date for ESPP         Apr. 27, 2025      
Maximum [Member]                
Stock-Based Compensation [Line Items]                
Percent of current fair market value, discount eligible employees may purchase common stock 10.00%              
Employee Stock Purchase Plan, maximum number of shares of common stock authorized for sale               1,000,000