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Retirement Benefits (Accumulated Benefit Obligation In Excess of Plan Assets) (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Other Postretirement Benefits    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets   $ 270
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 $ 55 51
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets   43
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 $ 31 34
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets   $ 0