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Stock-Based Compensation (Narrative) (Details) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended
Feb. 24, 2015
Feb. 28, 2019
Mar. 31, 2020
Mar. 31, 2019
Apr. 27, 2015
Stock-Based Compensation [Line Items]          
Stock-based compensation expense     $ 4 $ 4  
Stock-based compensation expense, net of tax     3 $ 3  
Total unrecognized compensation costs related to non-vested stock options and restricted share units     $ 48    
Weighted-average period of recognition of stock-based compensation cost     2 years 3 months 18 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     814,400    
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%