v3.20.4
Pension And Postretirement Benefits (Net Periodic Benefit Cost (Credit)) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]      
Net pension and postretirement cost (credit) $ 711 $ 2,762 $ (4,251)
Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Service cost – benefits earned during the period 1,029 1,019 1,116
Interest cost on projected benefit obligation 1,687 1,960 2,092
Expected return on assets (3,557) (3,561) (3,190)
Amortization of prior service credit (113) (113) (115)
Actuarial (gain) loss 2,404 3,088 (812)
Net pension and postretirement cost (credit) 1,450 2,393 (909)
Curtailment gain (1)    
Special termination benefits   81  
Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Service cost – benefits earned during the period 53 71 109
Interest cost on projected benefit obligation 416 675 778
Expected return on assets (178) (227) (304)
Amortization of prior service credit (2,329) (1,820) (1,635)
Actuarial (gain) loss 1,299 1,670 (2,290)
Net pension and postretirement cost (credit) $ (739) $ 369 $ (3,342)