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Pension and Other Postretirement Benefits (Schedule of Net Periodic Pension Cost) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]        
Service Cost $ 12 $ 9 $ 22 $ 19
Interest Cost 12 17 25 34
Expected Return on Plan Assets (36) (38) (71) (75)
Amortization of Actuarial Loss 14 12 27 23
Net Periodic Pension Cost (Credit) 2 0 3 1
Pension Plan [Member] | Qualified Plans [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 10 8 19 17
Interest Cost 12 16 24 32
Expected Return on Plan Assets (36) (38) (71) (75)
Amortization of Actuarial Loss 12 11 23 20
Net Periodic Pension Cost (Credit) (2) (3) (5) (6)
Supplemental Employee Retirement Plan [Member] | Nonqualified Plans [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service Cost 2 1 3 2
Interest Cost 0 1 1 2
Expected Return on Plan Assets 0 0 0 0
Amortization of Actuarial Loss 2 1 4 3
Net Periodic Pension Cost (Credit) $ 4 $ 3 $ 8 $ 7