v3.20.1
Pension and Other Postretirement Benefits - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Jan. 01, 2020
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Retirement plans, liability $ 1,920      
Retirement plans, current liability 60      
Retirement plans, benefit obligation 4,255      
Retirement plans, plan assets 2,335      
Establishment of retirement plans, AOCI $ 1,752      
Net periodic benefit cost   $ 26    
Service cost   6    
Multiemployer contribution expense     $ 28  
Forecast        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Net periodic benefit cost       $ 100
Service cost       $ 25
Pension benefits        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Net periodic benefit cost   21 1  
Service cost   5 0  
Multiemployer contribution expense   0 16  
Expected employer contributions, 2020   255    
Other postretirement benefits        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Net periodic benefit cost   6 0  
Service cost   1 0  
Multiemployer contribution expense   0 $ 5  
Expected employer contributions, 2020   $ 55