v3.26.3
Fair Value Measurement - Fair Value Measurement Inputs (Details) - USD ($)
$ in Millions
Sep. 30, 2026
Dec. 31, 2025
Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Investments, Fair Value Disclosure $ 28 $ 29
Trust Assets Fair Value Disclosure 62 71
Derivatives:    
Derivative Asset 0 0
Derivatives: [Abstract]    
Derivative Liability 0 0
Long-term debt, including current portion 0 0
Level 1    
Investment securities (current and long-term):    
Investments, Fair Value Disclosure 32 36
Trust Assets Fair Value Disclosure 3 22
Derivatives:    
Derivative Asset 42 50
Derivatives: [Abstract]    
Derivative Liability 1 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 139 139
Derivatives:    
Derivative Asset 72 239
Derivatives: [Abstract]    
Derivative Liability 44 96
Long-term debt, including current portion 9,036 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 0
Long-term debt, including current portion 0 0
Carrying Amount, Fair Value Disclosure    
Investment securities (current and long-term):    
Investments, Fair Value Disclosure 60 65
Trust Assets Fair Value Disclosure 204 232
Derivatives:    
Derivative Asset 114 289
Derivatives: [Abstract]    
Derivative Liability 45 107
Long-term debt, including current portion 9,398 9,379
Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Investments, Fair Value Disclosure 60 65
Trust Assets Fair Value Disclosure 204 232
Derivatives:    
Derivative Asset 114 289
Derivatives: [Abstract]    
Derivative Liability 45 107
Long-term debt, including current portion 9,036 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 59 217
Derivatives: [Abstract]    
Derivative Liability 43 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 59 217
Derivatives: [Abstract]    
Derivative Liability 43 84
Embedded Derivative Financial Instruments | Estimate of Fair Value Measurement    
Derivatives:    
Derivative Asset 59 217
Derivatives: [Abstract]    
Derivative Liability 43 84
Commodity Contract | Fair Value Measured at Net Asset Value Per Share    
Derivatives:    
Derivative Asset 0  
Derivatives: [Abstract]    
Derivative Liability 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 42  
Derivatives: [Abstract]    
Derivative Liability 1  
Commodity Contract | Level 1 | Futures and Swaps    
Derivatives:    
Derivative Asset   50
Commodity Contract | Level 2    
Derivatives:    
Derivative Asset 13  
Derivatives: [Abstract]    
Derivative Liability 1  
Commodity Contract | Level 2 | Futures and Swaps    
Derivatives:    
Derivative Asset   22
Commodity Contract | Level 3    
Derivatives:    
Derivative Asset 0  
Derivatives: [Abstract]    
Derivative Liability 0  
Commodity Contract | Level 3 | Futures and Swaps    
Derivatives:    
Derivative Asset   0
Commodity Contract | Carrying Amount, Fair Value Disclosure    
Derivatives:    
Derivative Asset 55  
Derivatives: [Abstract]    
Derivative Liability 2  
Commodity Contract | Carrying Amount, Fair Value Disclosure | Futures and Swaps    
Derivatives:    
Derivative Asset   72
Commodity Contract | Estimate of Fair Value Measurement    
Derivatives:    
Derivative Asset 55  
Derivatives: [Abstract]    
Derivative Liability 2  
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: [Abstract]    
Derivative Liability   0
Forward Contracts | Level 1    
Derivatives: [Abstract]    
Derivative Liability   11
Forward Contracts | Level 2    
Derivatives: [Abstract]    
Derivative Liability   12
Forward Contracts | Level 3    
Derivatives: [Abstract]    
Derivative Liability   0
Forward Contracts | Carrying Amount, Fair Value Disclosure    
Derivatives: [Abstract]    
Derivative Liability   23
Forward Contracts | Estimate of Fair Value Measurement    
Derivatives: [Abstract]    
Derivative Liability   23
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 32 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 32 36
Equity securities | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Marketable Securities 32 36
U.S. core fixed income fund | Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Marketable Securities 28 29
Trust Assets Fair Value Disclosure 62 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 28 29
Trust Assets Fair Value Disclosure 62 71
U.S. core fixed income fund | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Marketable Securities 28 29
Trust Assets Fair Value Disclosure 62 71
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 50 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 50 56
Government mortgage-backed securities | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 50 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 46 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 46 37
Government bonds | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 46 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 33 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 33 34
Corporate bonds | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 33 34
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 10 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 10 11
Asset-backed securities | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 10 11
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 3 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 3 22
Money market funds | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure $ 3 22
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