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Pensions and Other Postretirement Benefits - Narrative (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2023
USD ($)
investment_firm
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan's accumulated benefit obligation $ 2,000 $ 1,900  
Unfunded pension plans projected benefit obligation 300 275  
Unfunded pension plans accumulated benefit obligations $ 273 249  
Number of investment firms | investment_firm 13    
Multiemployer plan, contributions by employer $ 11 13 $ 21
Defined contribution plan, cost 25 22 $ 23
Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Trust-owned life insurance fair value $ 138 $ 122  
Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Pension plan assets target allocation for equity 50.00%    
Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Pension plan assets target allocation for equity 75.00%    
Debt securities      
Defined Benefit Plan Disclosure [Line Items]      
Weighted average asset allocation, by asset category 34.00% 36.00%  
Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Estimated net loss for defined pension plans amortized from AOCI into net periodic cost $ 16    
Assumed increases in per capita cost of covered health care benefits 6.50%    
Ultimate health care cost trend rate 5.00%    
Pension plan assets target allocation for equity 75.00%    
Assumed rate of return on pension plan assets 8.00%    
Expected contribution for the next fiscal year $ 22    
Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, future amortization of prior service cost (credit) (26)    
Expected contribution for the next fiscal year $ 31    
Other Postretirement Benefits | Defined Benefit Plan, Equity Securities      
Defined Benefit Plan Disclosure [Line Items]      
Weighted average asset allocation, by asset category 66.00% 64.00%