v3.25.2
Fair Value Measurement - Fair Value Measurement Inputs (Details) - USD ($)
$ in Millions
Jun. 30, 2025
Dec. 31, 2024
Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Investments, Fair Value Disclosure $ 28 $ 27
Trust Assets Fair Value Disclosure 69 66
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 21 9
Trust Assets Fair Value Disclosure 22 19
Derivatives:    
Derivative Asset 27 4
Derivatives: [Abstract]    
Derivative Liability 1 18
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 134 132
Derivatives:    
Derivative Asset 80 16
Derivatives: [Abstract]    
Derivative Liability 21 71
Long-term debt, including current portion 9,249 8,807
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 49 36
Trust Assets Fair Value Disclosure 225 217
Derivatives:    
Derivative Asset 107 20
Derivatives: [Abstract]    
Derivative Liability 22 89
Long-term debt, including current portion 9,251 8,948
Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Investments, Fair Value Disclosure 49 36
Trust Assets Fair Value Disclosure 225 217
Derivatives:    
Derivative Asset 107 20
Derivatives: [Abstract]    
Derivative Liability 22 89
Long-term debt, including current portion 9,249 8,807
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 66 10
Derivatives: [Abstract]    
Derivative Liability 19 60
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 66 10
Derivatives: [Abstract]    
Derivative Liability 19 60
Embedded Derivative Financial Instruments | Estimate of Fair Value Measurement    
Derivatives:    
Derivative Asset 66 10
Derivatives: [Abstract]    
Derivative Liability 19 60
Commodity Contract | Fair Value Measured at Net Asset Value Per Share    
Derivatives:    
Derivative Asset 0  
Derivatives: [Abstract]    
Derivative Liability 0 0
Commodity Contract | Level 1    
Derivatives:    
Derivative Asset 27  
Derivatives: [Abstract]    
Derivative Liability 0 17
Commodity Contract | Level 2    
Derivatives:    
Derivative Asset 14  
Derivatives: [Abstract]    
Derivative Liability 2 11
Commodity Contract | Level 3    
Derivatives:    
Derivative Asset 0  
Derivatives: [Abstract]    
Derivative Liability 0 0
Commodity Contract | Carrying Amount, Fair Value Disclosure    
Derivatives:    
Derivative Asset 41  
Derivatives: [Abstract]    
Derivative Liability 2 28
Commodity Contract | Estimate of Fair Value Measurement    
Derivatives:    
Derivative Asset 41  
Derivatives: [Abstract]    
Derivative Liability 2 28
Forward Contracts | Fair Value Measured at Net Asset Value Per Share    
Derivatives:    
Derivative Asset   0
Derivatives: [Abstract]    
Derivative Liability 0 0
Forward Contracts | Level 1    
Derivatives:    
Derivative Asset   4
Derivatives: [Abstract]    
Derivative Liability 1 1
Forward Contracts | Level 2    
Derivatives:    
Derivative Asset   6
Derivatives: [Abstract]    
Derivative Liability 0 0
Forward Contracts | Level 3    
Derivatives:    
Derivative Asset   0
Derivatives: [Abstract]    
Derivative Liability 0 0
Forward Contracts | Carrying Amount, Fair Value Disclosure    
Derivatives:    
Derivative Asset   10
Derivatives: [Abstract]    
Derivative Liability 1 1
Forward Contracts | Estimate of Fair Value Measurement    
Derivatives:    
Derivative Asset   10
Derivatives: [Abstract]    
Derivative Liability 1 1
U.S. core fixed income fund | Fair Value Measured at Net Asset Value Per Share    
Investment securities (current and long-term):    
Marketable Securities 28 27
Trust Assets Fair Value Disclosure 69 66
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 27
Trust Assets Fair Value Disclosure 69 66
U.S. core fixed income fund | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Marketable Securities 28 27
Trust Assets Fair Value Disclosure 69 66
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 21 9
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 21 9
Equity securities | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Marketable Securities 21 9
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 57 54
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 57 54
Government mortgage-backed securities | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 57 54
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 35 31
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 35 31
Corporate bonds | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 35 31
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 25 34
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 25 34
Government bonds | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 25 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 22 19
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 22 19
Money market funds | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 22 19
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 16 12
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 16 12
Asset-backed securities | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 16 12
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 0
Collateralized Mortgage Backed Securities | Level 1    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Collateralized Mortgage Backed Securities | Level 2    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 1 1
Collateralized Mortgage Backed Securities | Level 3    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 0 0
Collateralized Mortgage Backed Securities | Carrying Amount, Fair Value Disclosure    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure 1 1
Collateralized Mortgage Backed Securities | Estimate of Fair Value Measurement    
Investment securities (current and long-term):    
Trust Assets Fair Value Disclosure $ 1 $ 1