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Basis Of Presentation Stock Repurchases (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
3 Months Ended 6 Months Ended 28 Months Ended
Jun. 30, 2018
Jun. 30, 2018
Jun. 30, 2018
Feb. 26, 2018
Feb. 23, 2017
Feb. 24, 2016
Stock Repurchases [Line Items]            
Shares Repurchased and Retired During Period, Shares 4.1 7.8 24.3      
Shares Repurchased and Retired During Period, Value $ 101 $ 200 $ 674      
Weighted Average Market Price of Shares Repurchased and Retired During Period $ 24.94 $ 25.73 $ 27.80      
Stock Repurchase Program, Remaining Authorized Repurchase Amount $ 251 $ 251 $ 251      
Maximum | 2016 Stock Repurchase Plan            
Stock Repurchases [Line Items]            
Shares Authorized under Stock Repurchase Program,           $ 275
Maximum | 2017 Stock Repurchase Plan            
Stock Repurchases [Line Items]            
Shares Authorized under Stock Repurchase Program,         $ 300  
Maximum | 2018 Stock Repurchase Plan            
Stock Repurchases [Line Items]            
Shares Authorized under Stock Repurchase Program,       $ 350