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Retirement Plans (Reconciliation Of Benefit Obligations And Plan Or Trust Assets And Resulting Funded Status Of Defined Benefit Retirement Plans) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Pension Benefits      
Change in Benefit Obligation      
Benefit obligation at beginning of year $ (12,554) $ (13,236)  
Service cost (173) (210) $ (186)
Interest cost (456) (529) (532)
Amendments 0 6  
Actuarial gain (loss) (383) 685  
Settlement/curtailment/other (4) 195  
Benefits paid 548 535  
Benefit obligation at end of year (13,022) (12,554) (13,236)
Change in Plan/Trust Assets      
Fair value of assets at beginning of year 8,608 9,084  
Actual return on plan assets 694 (85)  
Employer contributions 208 187  
Settlement/curtailment/other 5 (54)  
Benefits paid (535) (524)  
Fair value of assets at end of year 8,980 8,608 9,084
Funded status at end of year (4,042) (3,946)  
Other Post-retirement Benefits      
Change in Benefit Obligation      
Benefit obligation at beginning of year (991) (1,130)  
Service cost (10) (11) (12)
Interest cost (34) (44) (52)
Amendments (13) (10)  
Actuarial gain (loss) (18) 104  
Settlement/curtailment/other (3) 35  
Benefits paid 64 65  
Benefit obligation at end of year (1,005) (991) (1,130)
Change in Plan/Trust Assets      
Fair value of assets at beginning of year 527 553  
Actual return on plan assets 9 13  
Employer contributions 5 0  
Settlement/curtailment/other 0 0  
Benefits paid (42) (39)  
Fair value of assets at end of year 499 527 $ 553
Funded status at end of year $ (506) $ (464)