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Incentive Plans (Schedule Of Performance Unit Activity) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Weighted Average Grant- Date Fair Value      
Common stock, shares issued 175,057,889 174,321,171  
Performance unit awards      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Outstanding at beginning of year, shares 119,169    
Units granted 86,483    
Units vested (89,437)    
Outstanding at end of year, shares 116,215 119,169  
Weighted Average Grant- Date Fair Value      
Outstanding (usd per share) $ 191.58 $ 251.92  
Units granted (usd per share) 165.84 $ 246.18 $ 258.27
Units vested (usd per share) $ 247.10    
Grant date fair value $ 22 $ 21 $ 18
Performance Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Units vested   (1,911)  
Weighted Average Grant- Date Fair Value      
Performance percentage of actual payout minimum 0.00%    
Performance percentage to reach maximum 250.00%    
Performance Units Service Period Lapsed [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Units vested (58,539)    
Officer | Performance unit awards      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Units vested (32,809)