v3.24.0.1
Benefit Plans: (Fair Value of Pension Plan Assets) (Details) - USD ($)
$ in Millions
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]      
Total assets $ 3 $ 3  
U S and International Equities      
Defined Benefit Plan Disclosure [Line Items]      
Investment in securities, percent 57.00% 57.00%  
U S and International Government Bonds      
Defined Benefit Plan Disclosure [Line Items]      
Investment in securities, percent 15.00% 15.00%  
Investment Funds Holding Corporate Bonds      
Defined Benefit Plan Disclosure [Line Items]      
Investment in securities, percent 15.00% 16.00%  
Real Estate and Other Money Markets      
Defined Benefit Plan Disclosure [Line Items]      
Investment in securities, percent 13.00% 12.00%  
Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Total assets $ 8,851 $ 7,939 $ 9,337
Pension Plan | Fair Value, Inputs, Level 1, 2 and 3      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 8,579 7,674  
Pension Plan | Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 117 79  
Pension Plan | Fair Value, Inputs, Level 1, 2 and 3 | U.S. securities      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 158 140  
Pension Plan | Fair Value, Inputs, Level 1, 2 and 3 | International securities      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 569 521  
Pension Plan | Fair Value, Inputs, Level 1, 2 and 3 | Investment Funds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 7,123 6,419  
Pension Plan | Fair Value, Inputs, Level 1, 2 and 3 | Government bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 255 178  
Pension Plan | Fair Value, Inputs, Level 1, 2 and 3 | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 320 302  
Pension Plan | Fair Value, Inputs, Level 1, 2 and 3 | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 37 35  
Pension Plan | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1)      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 6,713 6,029  
Pension Plan | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | Cash and cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 117 79  
Pension Plan | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | U.S. securities      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 158 140  
Pension Plan | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | International securities      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 569 521  
Pension Plan | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | Investment Funds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 5,366 4,870  
Pension Plan | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | Government bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 183 117  
Pension Plan | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 320 302  
Pension Plan | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 0 0  
Pension Plan | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 1,834 1,613  
Pension Plan | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total assets  
Pension Plan | Significant Other Observable Inputs (Level 2) | U.S. securities      
Defined Benefit Plan Disclosure [Line Items]      
Total assets  
Pension Plan | Significant Other Observable Inputs (Level 2) | International securities      
Defined Benefit Plan Disclosure [Line Items]      
Total assets  
Pension Plan | Significant Other Observable Inputs (Level 2) | Investment Funds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 1,757 1,549  
Pension Plan | Significant Other Observable Inputs (Level 2) | Government bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 72 61  
Pension Plan | Significant Other Observable Inputs (Level 2) | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets  
Pension Plan | Significant Other Observable Inputs (Level 2) | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 5 3  
Pension Plan | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 32 32  
Pension Plan | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total assets  
Pension Plan | Significant Unobservable Inputs (Level 3) | U.S. securities      
Defined Benefit Plan Disclosure [Line Items]      
Total assets  
Pension Plan | Significant Unobservable Inputs (Level 3) | International securities      
Defined Benefit Plan Disclosure [Line Items]      
Total assets  
Pension Plan | Significant Unobservable Inputs (Level 3) | Investment Funds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets  
Pension Plan | Significant Unobservable Inputs (Level 3) | Government bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets  
Pension Plan | Significant Unobservable Inputs (Level 3) | Corporate bonds      
Defined Benefit Plan Disclosure [Line Items]      
Total assets  
Pension Plan | Significant Unobservable Inputs (Level 3) | Other      
Defined Benefit Plan Disclosure [Line Items]      
Total assets 32 32  
Pension Plan | Fair Value Measured at Net Asset Value Per Share      
Defined Benefit Plan Disclosure [Line Items]      
Total assets $ 272 $ 265