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Pension and Other Postretirement Employee Benefits (OPEB) Plans - Narrative (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2023
USD ($)
corporateBond
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Defined Benefit Plan Disclosure [Line Items]      
Market-related value of assets held in trust, realized and unrealized gains or losess, included in preceding period, related to vesting percentage 25.00%    
Increase (decrease) in obligation, pension benefits $ 1    
Service cost, amortization period 2 years    
Fair value of assets $ 28 $ 30  
Assumed discount rate, number of corporate bonds used to derive yield curve | corporateBond 509    
Maximum amount employee may contribute if earnings are less that IRS threshold 75.00%    
Percent of employees pay eligible for contribution to plan, minimum 1.00%    
Percent of employees pay eligible for contribution to plan, maximum 20.00%    
Percent of employees pay eligible to be matched by employer 6.00%    
Employer contributions to the thrift plan $ 33 33 $ 34
Pension costs      
Defined Benefit Plan Disclosure [Line Items]      
Net actuarial gain (loss) (5) 16 24
Fair value of assets 285 320 470
Employer contributions 0 0 1
Expected future employer contributions to retirement plan 14    
Pension costs | Fair Value, Recurring      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at net asset value 285 320  
Pension costs | Cash commingled trusts | Fair Value, Recurring      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at net asset value 4 4  
OPEB costs      
Defined Benefit Plan Disclosure [Line Items]      
Net actuarial gain (loss) 0 22 7
Fair value of assets 12 29 39
Employer contributions 9 9 $ 9
Expected future employer contributions to retirement plan 9    
OPEB costs | Cash commingled trusts | Fair Value, Recurring      
Defined Benefit Plan Disclosure [Line Items]      
Total assets measured at net asset value 9 28  
OPEB costs | Municipal Bond and Cash Equivalent Mutual Fund | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of assets $ 3 $ 1  
Qualified Plan      
Defined Benefit Plan Disclosure [Line Items]      
Percent of employees contribution matched by employer 100.00%    
Traditional Retirement Plan Formula of Retirement Plan      
Defined Benefit Plan Disclosure [Line Items]      
Percent of employees contribution matched by employer 75.00%