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Benefit Plans (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Pension Benefits [Member]        
Components of Net Periodic Benefit [Abstract]        
Service cost   $ 1 $ 1 $ 2
Interest cost $ 18 23 36 46
Expected return on plan assets (43) (44) (86) (87)
Amortization of unrecognized net loss 13 12 25 23
Amortization of unrecognized prior service benefit   1   1
Settlement charge 2 3 2 7
Net periodic (benefit) cost (10) (4) (22) (8)
Other Postretirement Benefits [Member]        
Components of Net Periodic Benefit [Abstract]        
Interest cost 1 1 1 1
Expected return on plan assets   (1) (1) (2)
Net periodic (benefit) cost $ 1 $ 0 $ 0 $ (1)