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Retirement Benefits (Fair Value of Plan Assets) (Details) - USD ($)
$ in Millions
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Accumulated benefit obligation $ 138 $ 148 $ 195
Fair value of plan assets 277 259 311
Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Accumulated benefit obligation   22 50
Fair value of plan assets 22 20  
Cash and Cash Equivalents [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 13 19  
Cash and Cash Equivalents [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 2 2  
Mutual Fund [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 166 [1] 146 [2]  
Mutual Fund [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 20 [3] 18 [4]  
Fixed Income Securities [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 98 94  
Level 1 [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 179 165  
Level 1 [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 22 20  
Level 1 [Member] | Cash and Cash Equivalents [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 13 19  
Level 1 [Member] | Cash and Cash Equivalents [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 2 2  
Level 1 [Member] | Mutual Fund [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 166 [1] 146 [2]  
Level 1 [Member] | Mutual Fund [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 20 [3] 18 [4]  
Level 1 [Member] | Fixed Income Securities [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 0  
Level 2 [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 98 94  
Level 2 [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 0  
Level 2 [Member] | Cash and Cash Equivalents [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 0  
Level 2 [Member] | Cash and Cash Equivalents [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 0  
Level 2 [Member] | Mutual Fund [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 [1] 0 [2]  
Level 2 [Member] | Mutual Fund [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 [3] 0 [4]  
Level 2 [Member] | Fixed Income Securities [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 98 94  
Level 3 [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 0  
Level 3 [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 0  
Level 3 [Member] | Cash and Cash Equivalents [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 0  
Level 3 [Member] | Cash and Cash Equivalents [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 0  
Level 3 [Member] | Mutual Fund [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 [1] 0 [2]  
Level 3 [Member] | Mutual Fund [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 [3] 0 [4]  
Level 3 [Member] | Fixed Income Securities [Member] | Other Postretirement Benefits      
Fair Value of Plan Assets [Line Items]      
Fair value of plan assets 0 0  
Funded Plans [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Projected benefit obligation 23 22  
Accumulated benefit obligation 23 22  
Fair value of plan assets 22 20 44
Unfunded Plans [Member] | Pension Benefits      
Fair Value of Plan Assets [Line Items]      
Projected benefit obligation 15 19  
Accumulated benefit obligation 17 19 26
Fair value of plan assets $ 0 $ 0 $ 0
[1] Primarily composed of market index funds as of December 31, 2023.
[2] Primarily composed of market index funds as of December 31, 2022.
[3] Comprised of approximately 100% equities as of December 31, 2023.
[4] Comprised of approximately 100% equities as of December 31, 2022.