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Basis Of Presentation Stock Repurchases (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
3 Months Ended 13 Months Ended
Mar. 31, 2017
Mar. 31, 2017
Feb. 23, 2017
Feb. 24, 2016
Stock Repurchases [Line Items]        
Shares Repurchased and Retired During Period, Shares 2.2 9.3    
Shares Repurchased and Retired During Period, Value $ 60 $ 259    
Weighted Average Market Price of Shares Repurchased and Retired During Period $ 27.82 $ 27.93    
Maximum        
Stock Repurchases [Line Items]        
Shares Authorized under Stock Repurchase Program,     $ 300 $ 275
2016 Stock Repurchase Plan [Member]        
Stock Repurchases [Line Items]        
Stock Repurchase Program, Remaining Authorized Repurchase Amount $ 16 $ 16    
2017 Stock Repurchase Plan [Member]        
Stock Repurchases [Line Items]        
Stock Repurchase Program, Remaining Authorized Repurchase Amount $ 300 $ 300