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Retirement Benefits (Net Periodic Benefit Costs Schedule) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Pension Benefits    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Service Cost $ 0 $ 0
Defined Benefit Plan, Interest Cost 3 3
Defined Benefit Plan, Expected Return (Loss) on Plan Assets 2 2
Defined Benefit Plan, Amortization of Prior Service Cost (Credit) 0 0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) 1 1
Other Postretirement Benefits    
Defined Benefit Plan Disclosure [Line Items]    
Defined Benefit Plan, Service Cost 1 1
Defined Benefit Plan, Interest Cost 5 7
Defined Benefit Plan, Expected Return (Loss) on Plan Assets 11 10
Defined Benefit Plan, Amortization of Prior Service Cost (Credit) 19 26
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) $ 14 $ 24