Fair Value Measurement - Fair Value Measurement Inputs (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2016
Investment securities (current and long-term):
Other Assets, Current	$ 385	$ 375
Other assets	1,846	1,810
Derivatives:
Derivative Asset	136	80
Derivatives: [Abstract]
Derivative Liability	19	24
Deepwater Gulf of Mexico Interests | Freeport-McMoRan Oil & Gas
Derivatives:
Discontinued Operation, Contingent Receivable			$ 150
Fair Value Measured at Net Asset Value Per Share
Investment securities (current and long-term):
Investments, Fair Value Disclosure	26	27
Trust Assets Fair Value Disclosure	65	65
Derivatives:
Derivative Asset	0	0
Discontinued Operation, Contingent Receivable	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	7	6
Trust Assets Fair Value Disclosure	20	17
Derivatives:
Derivative Asset	8	3
Discontinued Operation, Contingent Receivable	0	0
Derivatives: [Abstract]
Derivative Liability	2	1
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	126	130
Derivatives:
Derivative Asset	128	77
Discontinued Operation, Contingent Receivable	0	0
Derivatives: [Abstract]
Derivative Liability	17	23
Long-term debt, including current portion	9,301	9,364
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
Discontinued Operation, Contingent Receivable	40	42
Derivatives: [Abstract]
Derivative Liability	0	0
Long-term debt, including current portion	0	0
Estimate of Fair Value Measurement
Investment securities (current and long-term):
Investments, Fair Value Disclosure	33	33
Trust Assets Fair Value Disclosure	211	212
Derivatives:
Derivative Asset	136	80
Discontinued Operation, Contingent Receivable	40	42
Derivatives: [Abstract]
Derivative Liability	19	24
Long-term debt, including current portion	9,301	9,364
Carrying Amount, Fair Value Disclosure
Investment securities (current and long-term):
Investments, Fair Value Disclosure	33	33
Trust Assets Fair Value Disclosure	211	212
Derivatives:
Derivative Asset	136	80
Discontinued Operation, Contingent Receivable	47	50
Derivatives: [Abstract]
Derivative Liability	19	24
Long-term debt, including current portion	9,425	9,422
Embedded Derivative Financial Instruments
Derivatives:
Derivative Asset	122	76
Derivatives: [Abstract]
Derivative Liability	16	23
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	122	76
Derivatives: [Abstract]
Derivative Liability	16	23
Embedded Derivative Financial Instruments | Level 3
Derivatives:
Derivative Asset	0	0
Derivatives: [Abstract]
Derivative Liability	0	0
Embedded Derivative Financial Instruments | Estimate of Fair Value Measurement
Derivatives:
Derivative Asset	122	76
Derivatives: [Abstract]
Derivative Liability	16	23
Embedded Derivative Financial Instruments | Carrying Amount, Fair Value Disclosure
Derivatives:
Derivative Asset	122	76
Derivatives: [Abstract]
Derivative Liability	16	23
Forward Contracts | Level 1
Derivatives:
Derivative Asset	0
Forward Contracts | Level 2
Derivatives:
Derivative Asset	1
Forward Contracts | Level 3
Derivatives:
Derivative Asset	0
Forward Contracts | Estimate of Fair Value Measurement
Derivatives:
Derivative Asset	1
Forward Contracts | Carrying Amount, Fair Value Disclosure
Derivatives:
Derivative Asset	1
Commodity Contract
Derivatives:
Derivative Asset	14	4
Derivatives: [Abstract]
Derivative Liability	3	1
Commodity Contract | Fair Value Measured at Net Asset Value Per Share
Derivatives:
Derivative Asset	0	0
Commodity Contract | Fair Value Measured at Net Asset Value Per Share | Forward Contracts
Derivatives: [Abstract]
Derivative Liability	0	0
Commodity Contract | Level 1
Derivatives:
Derivative Asset		3
Commodity Contract | Level 1 | Forward Contracts
Derivatives: [Abstract]
Derivative Liability	2	1
Commodity Contract | Level 2
Derivatives:
Derivative Asset		1
Commodity Contract | Level 2 | Forward Contracts
Derivatives: [Abstract]
Derivative Liability	1	0
Commodity Contract | Level 3
Derivatives:
Derivative Asset		0
Commodity Contract | Level 3 | Forward Contracts
Derivatives: [Abstract]
Derivative Liability	0	0
Commodity Contract | Estimate of Fair Value Measurement
Derivatives:
Derivative Asset		4
Commodity Contract | Estimate of Fair Value Measurement | Forward Contracts
Derivatives: [Abstract]
Derivative Liability	3	1
Commodity Contract | Carrying Amount, Fair Value Disclosure
Derivatives:
Derivative Asset		4
Commodity Contract | Carrying Amount, Fair Value Disclosure | Forward Contracts
Derivatives: [Abstract]
Derivative Liability	3	1
Future | Level 1
Derivatives:
Derivative Asset	8
Future | Level 2
Derivatives:
Derivative Asset	5
Future | Level 3
Derivatives:
Derivative Asset	0
Future | Estimate of Fair Value Measurement
Derivatives:
Derivative Asset	13
Future | Carrying Amount, Fair Value Disclosure
Derivatives:
Derivative Asset	13
U.S. core fixed income fund | Fair Value Measured at Net Asset Value Per Share
Investment securities (current and long-term):
Marketable Securities	26	27
Trust Assets Fair Value Disclosure	65	65
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 | Estimate of Fair Value Measurement
Investment securities (current and long-term):
Marketable Securities	26	27
Trust Assets Fair Value Disclosure	65	65
U.S. core fixed income fund | Carrying Amount, Fair Value Disclosure
Investment securities (current and long-term):
Marketable Securities	26	27
Trust Assets Fair Value Disclosure	65	65
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	7	6
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 | Estimate of Fair Value Measurement
Investment securities (current and long-term):
Marketable Securities	7	6
Equity securities | Carrying Amount, Fair Value Disclosure
Investment securities (current and long-term):
Marketable Securities	7	6
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	48	51
Government mortgage-backed securities | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Government mortgage-backed securities | Estimate of Fair Value Measurement
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	48	51
Government mortgage-backed securities | Carrying Amount, Fair Value Disclosure
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	48	51
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	32	37
Government bonds | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Government bonds | Estimate of Fair Value Measurement
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	32	37
Government bonds | Carrying Amount, Fair Value Disclosure
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	32	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	32	29
Corporate bonds | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Corporate bonds | Estimate of Fair Value Measurement
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	32	29
Corporate bonds | Carrying Amount, Fair Value Disclosure
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	32	29
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	17
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 | Estimate of Fair Value Measurement
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	20	17
Money market funds | Carrying Amount, Fair Value Disclosure
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	20	17
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	13	12
Asset-backed securities | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Asset-backed securities | Estimate of Fair Value Measurement
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	13	12
Asset-backed securities | Carrying Amount, Fair Value Disclosure
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	13	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 | Estimate of Fair Value Measurement
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	1	1
Collateralized Mortgage Backed Securities | Carrying Amount, Fair Value Disclosure
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	1	1
Bank Time Deposits | Carrying Amount, Fair Value Disclosure
Investment securities (current and long-term):
Other Assets, Current		97
Other assets	147	$ 145
Fair Value, Recurring [Member] | Forward Contracts | Estimate of Fair Value Measurement
Derivatives:
Derivative Asset	$ 0