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Retirement Benefits (Accumulated Benefit Obligation In Excess of Plan Assets) (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Other Postretirement Benefits    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation $ 198 $ 156
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets 241 257
Funded Plans [Member] | Pension Benefits    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation 0 1
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation 1 1
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets 1 1
Unfunded Plans [Member] | Pension Benefits    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation 37 47
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation 37 47
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets $ 0 $ 0