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Stock Based Compensation (Options Exercised) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Payment Arrangement [Abstract]      
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number   231,933  
Total Intrinsic Value of Options Exercised $ 0 $ 5 $ 2
Cash Received from Options Exercised 0 8 4
Tax Benefit Realized from Options Exercised $ 0 $ 1 $ 0
Share-based Payment Arrangement, Option, Exercise Price Range, Outstanding, Weighted Average Exercise Price   $ 33.49