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Retirement Benefits (Schedule Of Potential Changes In Key Assumptions) (Details)
$ in Millions
12 Months Ended
Dec. 31, 2017
USD ($)
Pension Benefits  
Defined Benefit Plan Disclosure [Line Items]  
Service Cost and Interest Cost, .25% decrease in discount rate $ (1)
Benefit Obligation, .25% decrease in discount rate 157
Service Cost and Interest Cost, .25% increase in salary rate 2
Benefit Obligation, .25% increase in salary rate 15
Postretirement Benefits  
Defined Benefit Plan Disclosure [Line Items]  
Service Cost and Interest Cost, .25% decrease in discount rate 0
Benefit Obligation, .25% decrease in discount rate 44
Service Cost and Interest Cost, 1.00% increase in annual medical trend 4
Benefit Obligation, 1.00% increase in annual medical trend 71
Service Cost and Interest Cost, 1.00% decrease in annual medical trend (4)
Benefit Obligation, 1.00% decrease in annual medical trend $ (71)