v3.26.1
Fair Value Measurement - Fair Value Measurement Inputs (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Investments, Fair Value Disclosure $ 30 $ 29
Trust Assets Fair Value Disclosure 72 71
Derivatives:    
Derivative Asset 0 0
Derivatives: [Abstract]    
Derivative Liability   0
Long-term debt, including current portion 0 0
Level 1    
Investment securities (current and long-term):    
Investments, Fair Value Disclosure 29 36
Trust Assets Fair Value Disclosure 20 22
Derivatives:    
Derivative Asset 42 50
Derivatives: [Abstract]    
Derivative Liability   11
Long-term debt, including current portion 0 0
Level 2    
Investment securities (current and long-term):    
Investments, Fair Value Disclosure 0 0
Trust Assets Fair Value Disclosure 142 139
Derivatives:    
Derivative Asset 44 239
Derivatives: [Abstract]    
Derivative Liability   96
Long-term debt, including current portion 9,376 9,493
Level 3    
Investment securities (current and long-term):    
Investments, Fair Value Disclosure 0 0
Trust Assets Fair Value Disclosure 0 0
Derivatives:    
Derivative Asset 0 0
Derivatives: [Abstract]    
Derivative Liability   0
Long-term debt, including current portion 0 0
Carrying Amount, Fair Value Disclosure    
Investment securities (current and long-term):    
Investments, Fair Value Disclosure 59 65
Trust Assets Fair Value Disclosure 234 232
Derivatives:    
Derivative Asset 86 289
Derivatives: [Abstract]    
Derivative Liability   107
Long-term debt, including current portion 9,386 9,379
Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Investments, Fair Value Disclosure 59 65
Trust Assets Fair Value Disclosure 234 232
Derivatives:    
Derivative Asset 86 289
Derivatives: [Abstract]    
Derivative Liability   107
Long-term debt, including current portion 9,376 9,493
Embedded Derivative Financial Instruments | Fair Value Measured at Net Asset Value Per Share    
Derivatives:    
Derivative Asset 0 0
Derivatives: [Abstract]    
Derivative Liability 0 0
Embedded Derivative Financial Instruments | Level 1    
Derivatives:    
Derivative Asset 0 0
Derivatives: [Abstract]    
Derivative Liability 0 0
Embedded Derivative Financial Instruments | Level 2    
Derivatives:    
Derivative Asset 29 217
Derivatives: [Abstract]    
Derivative Liability 29 84
Embedded Derivative Financial Instruments | Level 3    
Derivatives:    
Derivative Asset 0 0
Derivatives: [Abstract]    
Derivative Liability 0 0
Embedded Derivative Financial Instruments | Carrying Amount, Fair Value Disclosure    
Derivatives:    
Derivative Asset 29 217
Derivatives: [Abstract]    
Derivative Liability 29 84
Embedded Derivative Financial Instruments | Estimate of Fair Value Measurement    
Derivatives:    
Derivative Asset 29 217
Derivatives: [Abstract]    
Derivative Liability 29 84
Commodity Contract | Fair Value Measured at Net Asset Value Per Share    
Derivatives:    
Derivative Asset 0  
Commodity Contract | Fair Value Measured at Net Asset Value Per Share | Futures and Swaps    
Derivatives:    
Derivative Asset   0
Commodity Contract | Level 1    
Derivatives:    
Derivative Asset 40  
Commodity Contract | Level 1 | Futures and Swaps    
Derivatives:    
Derivative Asset   50
Commodity Contract | Level 2    
Derivatives:    
Derivative Asset 13  
Commodity Contract | Level 2 | Futures and Swaps    
Derivatives:    
Derivative Asset   22
Commodity Contract | Level 3    
Derivatives:    
Derivative Asset 0  
Commodity Contract | Level 3 | Futures and Swaps    
Derivatives:    
Derivative Asset   0
Commodity Contract | Carrying Amount, Fair Value Disclosure    
Derivatives:    
Derivative Asset 53  
Commodity Contract | Carrying Amount, Fair Value Disclosure | Futures and Swaps    
Derivatives:    
Derivative Asset   72
Commodity Contract | Estimate of Fair Value Measurement    
Derivatives:    
Derivative Asset 53  
Commodity Contract | Estimate of Fair Value Measurement | Futures and Swaps    
Derivatives:    
Derivative Asset   72
Forward Contracts | Fair Value Measured at Net Asset Value Per Share    
Derivatives:    
Derivative Asset 0  
Derivatives: [Abstract]    
Derivative Liability   0
Forward Contracts | Level 1    
Derivatives:    
Derivative Asset 2  
Derivatives: [Abstract]    
Derivative Liability   11
Forward Contracts | Level 2    
Derivatives:    
Derivative Asset 2  
Derivatives: [Abstract]    
Derivative Liability   12
Forward Contracts | Level 3    
Derivatives:    
Derivative Asset 0  
Derivatives: [Abstract]    
Derivative Liability   0
Forward Contracts | Carrying Amount, Fair Value Disclosure    
Derivatives:    
Derivative Asset 4  
Derivatives: [Abstract]    
Derivative Liability   23
Forward Contracts | Estimate of Fair Value Measurement    
Derivatives:    
Derivative Asset 4  
Derivatives: [Abstract]    
Derivative Liability   23
U.S. core fixed income fund | Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Marketable Securities 30 29
Trust Assets Fair Value Disclosure 72 71
U.S. core fixed income fund | Level 1    
Investment securities (current and long-term):    
Marketable Securities 0 0
Trust Assets Fair Value Disclosure 0 0
U.S. core fixed income fund | Level 2    
Investment securities (current and long-term):    
Marketable Securities 0 0
Trust Assets Fair Value Disclosure 0 0
U.S. core fixed income fund | Level 3    
Investment securities (current and long-term):    
Marketable Securities 0 0
Trust Assets Fair Value Disclosure 0 0
U.S. core fixed income fund | Carrying Amount, Fair Value Disclosure    
Investment securities (current and long-term):    
Marketable Securities 30 29
Trust Assets Fair Value Disclosure 72 71
U.S. core fixed income fund | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Marketable Securities 30 29
Trust Assets Fair Value Disclosure 72 71
Equity securities | Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Marketable Securities 0 0
Equity securities | Level 1    
Investment securities (current and long-term):    
Marketable Securities 29 36
Equity securities | Level 2    
Investment securities (current and long-term):    
Marketable Securities 0 0
Equity securities | Level 3    
Investment securities (current and long-term):    
Marketable Securities 0 0
Equity securities | Carrying Amount, Fair Value Disclosure    
Investment securities (current and long-term):    
Marketable Securities 29 36
Equity securities | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Marketable Securities 29 36
Government mortgage-backed securities | Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Government mortgage-backed securities | Level 1    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Government mortgage-backed securities | Level 2    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 47 56
Government mortgage-backed securities | Level 3    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Government mortgage-backed securities | Carrying Amount, Fair Value Disclosure    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 47 56
Government mortgage-backed securities | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 47 56
Government bonds | Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Government bonds | Level 1    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Government bonds | Level 2    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 47 37
Government bonds | Level 3    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Government bonds | Carrying Amount, Fair Value Disclosure    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 47 37
Government bonds | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 47 37
Corporate bonds | Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Corporate bonds | Level 1    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Corporate bonds | Level 2    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 37 34
Corporate bonds | Level 3    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Corporate bonds | Carrying Amount, Fair Value Disclosure    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 37 34
Corporate bonds | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 37 34
Money market funds | Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Money market funds | Level 1    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 20 22
Money market funds | Level 2    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Money market funds | Level 3    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Money market funds | Carrying Amount, Fair Value Disclosure    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 20 22
Money market funds | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 20 22
Asset-backed securities | Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Asset-backed securities | Level 1    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Asset-backed securities | Level 2    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 11 11
Asset-backed securities | Level 3    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Asset-backed securities | Carrying Amount, Fair Value Disclosure    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 11 11
Asset-backed securities | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure $ 11 11
Collateralized Mortgage Backed Securities | Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure   0
Collateralized Mortgage Backed Securities | Level 1    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure   0
Collateralized Mortgage Backed Securities | Level 2    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure   1
Collateralized Mortgage Backed Securities | Level 3    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure   0
Collateralized Mortgage Backed Securities | Carrying Amount, Fair Value Disclosure    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure   1
Collateralized Mortgage Backed Securities | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure   $ 1