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Retirement Plans (Details) - USD ($)
 3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Net Periodic Pension And OPEB Cost [Abstract]    
Changes in fair value 5 years  
Other comprehensive income defined benefit plans $ (25,000,000) $ (22,000,000)
Defined Benefit Plans [Member]    
Net Periodic Pension And OPEB Cost [Abstract]    
Service cost 30,000,000 27,000,000
Interest cost 26,000,000 34,000,000
Expected return on plan assets (67,000,000) (70,000,000)
Amortization of actuarial loss 36,000,000 28,000,000
Net periodic cost 25,000,000 19,000,000
Voluntary cash contributions to qualified pension plan 0  
OPEB [Member]    
Net Periodic Pension And OPEB Cost [Abstract]    
Interest cost 1,000,000 1,000,000
Amortization of prior service cost (4,000,000) (3,000,000)
Amortization of actuarial loss 2,000,000 $ 2,000,000
Net periodic cost $ (1,000,000)