Fair Value Measurement (Fair Value Measurement Inputs) (Details) $ in Millions	3 Months Ended	9 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($) $ / bbl	Dec. 31, 2019 USD ($) $ / bbl	Dec. 31, 2016 USD ($) $ / bbl
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Other Assets, Current		$ 419			$ 655
Other assets		1,654			1,885
Proceeds from Sale of Other Assets, contingent consideration		146	$ 102
Derivative Liability, Fair Value, Gross Liability		20			21
Investment securities (current and long-term):
Marketable Securities		0
Derivatives:
Derivative Asset		62			74
Derivatives: [Abstract]
Derivative Liability		17			21
Fair Value Measured at Net Asset Value Per Share [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Discontinued Operation, Contingent Receivable		0			0
Investment securities (current and long-term):
Investments, Fair Value Disclosure		29			27
Trust Assets Fair Value Disclosure		64			59
Derivatives:
Derivative Asset		0			0
Derivatives: [Abstract]
Derivative Liability					0
Long-term debt, including current portion		0			0
Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Discontinued Operation, Contingent Receivable		0			0
Investment securities (current and long-term):
Investments, Fair Value Disclosure		6			4
Trust Assets Fair Value Disclosure		9			3
Derivatives:
Derivative Asset		13			5
Derivatives: [Abstract]
Derivative Liability					0
Long-term debt, including current portion		0			0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Discontinued Operation, Contingent Receivable		0			0
Investment securities (current and long-term):
Investments, Fair Value Disclosure		0			0
Trust Assets Fair Value Disclosure		138			134
Derivatives:
Derivative Asset		52			80
Derivatives: [Abstract]
Derivative Liability					21
Long-term debt, including current portion		10,735			10,239
Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Discontinued Operation, Contingent Receivable		84			108
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
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Discontinued Operation, Contingent Receivable		84			108
Investment securities (current and long-term):
Investments, Fair Value Disclosure		35			31
Trust Assets Fair Value Disclosure		211			196
Derivatives:
Derivative Asset		65			85
Derivatives: [Abstract]
Derivative Liability					21
Long-term debt, including current portion		10,735			10,239
Carrying Amount, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Discontinued Operation, Contingent Receivable		113			122
Investment securities (current and long-term):
Investments, Fair Value Disclosure		35			31
Trust Assets Fair Value Disclosure		211			196
Derivatives:
Derivative Asset		65			85
Derivatives: [Abstract]
Derivative Liability					21
Long-term debt, including current portion		10,030			9,826
Embedded Derivative Financial Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivative Liability, Fair Value, Gross Liability		20			20
Derivatives:
Derivative Asset		48			68
Derivatives: [Abstract]
Derivative Liability		17			20
Embedded Derivative Financial Instruments [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Derivatives:
Derivative Asset		0			0
Derivatives: [Abstract]
Derivative Liability		0			0
Embedded Derivative Financial Instruments [Member] | Level 1
Derivatives:
Derivative Asset		0			0
Derivatives: [Abstract]
Derivative Liability		0			0
Embedded Derivative Financial Instruments [Member] | Level 2
Derivatives:
Derivative Asset		51			68
Derivatives: [Abstract]
Derivative Liability		20			20
Embedded Derivative Financial Instruments [Member] | Level 3
Derivatives:
Derivative Asset		0			0
Derivatives: [Abstract]
Derivative Liability		0			0
Embedded Derivative Financial Instruments [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset		51			68
Derivatives: [Abstract]
Derivative Liability		20			20
Embedded Derivative Financial Instruments [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset		51			68
Derivatives: [Abstract]
Derivative Liability		20			20
Forward Contracts [Member] | Level 1
Derivatives:
Derivative Asset		1
Forward Contracts [Member] | Level 2
Derivatives:
Derivative Asset		0
Forward Contracts [Member] | Level 3
Derivatives:
Derivative Asset		0
Forward Contracts [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset		1
Forward Contracts [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset		1
Commodity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivative Liability, Fair Value, Gross Liability		0			1
Derivatives:
Derivative Asset		14			6
Derivatives: [Abstract]
Derivative Liability		0			1
Commodity Contract [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Derivatives:
Derivative Asset		0			0
Derivatives: [Abstract]
Derivative Liability					0
Commodity Contract [Member] | Level 1
Derivatives:
Derivative Asset					5
Derivatives: [Abstract]
Derivative Liability					0
Commodity Contract [Member] | Level 2
Derivatives:
Derivative Asset					1
Derivatives: [Abstract]
Derivative Liability					1
Commodity Contract [Member] | Level 3
Derivatives:
Derivative Asset					0
Derivatives: [Abstract]
Derivative Liability					0
Commodity Contract [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset					6
Derivatives: [Abstract]
Derivative Liability					1
Commodity Contract [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset					6
Derivatives: [Abstract]
Derivative Liability					1
Future [Member] | Level 1
Derivatives:
Derivative Asset		12
Future [Member] | Level 2
Derivatives:
Derivative Asset		1
Future [Member] | Level 3
Derivatives:
Derivative Asset		0
Future [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset		13
Future [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset		13
Africa and onshore California [Member] | Commodity Contract [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Derivatives:
Derivative Asset					0
Africa and onshore California [Member] | Commodity Contract [Member] | Level 1
Derivatives:
Derivative Asset					0
Africa and onshore California [Member] | Commodity Contract [Member] | Level 2
Derivatives:
Derivative Asset					11
Africa and onshore California [Member] | Commodity Contract [Member] | Level 3
Derivatives:
Derivative Asset					0
Africa and onshore California [Member] | Commodity Contract [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset					11
Africa and onshore California [Member] | Commodity Contract [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset					11
U.S. core fixed income fund [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Investment securities (current and long-term):
Marketable Securities		29			27
Trust Assets Fair Value Disclosure		64			59
U.S. core fixed income fund [Member] | 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 [Member] | 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 [Member] | 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 [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Marketable Securities		29			27
Trust Assets Fair Value Disclosure		64			59
U.S. core fixed income fund [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Marketable Securities		29			27
Trust Assets Fair Value Disclosure		64			59
Equity securities | Fair Value Measured at Net Asset Value Per Share [Member]
Investment securities (current and long-term):
Marketable Securities					0
Equity securities | Level 1
Investment securities (current and long-term):
Marketable Securities		6			4
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 [Member]
Investment securities (current and long-term):
Marketable Securities		6			4
Equity securities | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Marketable Securities		6			4
Government bonds | Fair Value Measured at Net Asset Value Per Share [Member]
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		42			36
Government bonds | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Government bonds | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		42			36
Government bonds | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		42			36
Corporate bonds [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Corporate bonds [Member] | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Corporate bonds [Member] | Level 2
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		43			33
Corporate bonds [Member] | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Corporate bonds [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		43			33
Corporate bonds [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		43			33
Government mortgage-backed securities [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Government mortgage-backed securities [Member] | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Government mortgage-backed securities [Member] | Level 2
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		33			43
Government mortgage-backed securities [Member] | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Government mortgage-backed securities [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		33			43
Government mortgage-backed securities [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		33			43
Asset-backed securities [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Asset-backed securities [Member] | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Asset-backed securities [Member] | Level 2
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		15			14
Asset-backed securities [Member] | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Asset-backed securities [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		15			14
Asset-backed securities [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		15			14
Money market funds [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Money market funds [Member] | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		9			3
Money market funds [Member] | Level 2
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Money market funds [Member] | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Money market funds [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		9			3
Money market funds [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		9			3
Collateralized Mortgage Backed Securities [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Collateralized Mortgage Backed Securities [Member] | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Collateralized Mortgage Backed Securities [Member] | Level 2
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		4			7
Collateralized Mortgage Backed Securities [Member] | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Collateralized Mortgage Backed Securities [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		4			7
Collateralized Mortgage Backed Securities [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		4			7
Municipal bonds [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Municipal bonds [Member] | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Municipal bonds [Member] | Level 2
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		1			1
Municipal bonds [Member] | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		0			0
Municipal bonds [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		1			1
Municipal bonds [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure		1			1
Bank Time Deposits [Member] | Carrying Amount, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Other Assets, Current		103			100
Other assets		148			157
Not Designated as Hedging Instrument [Member] | Embedded Derivative Financial Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivative Liability, Fair Value, Gross Liability		20			20
Freeport-McMoRan Oil & Gas | Onshore California [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Other assets		0			11
Discontinued Operation, Contingent Receivable						$ 150
Proceeds from Sale of Other Assets, contingent consideration				$ 50
Derivatives:
Discontinued Operation, Contingent Receivable, Per Year		50
Freeport-McMoRan Oil & Gas | Deepwater Gulf of Mexico Interests [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Other Assets, Current		12			18
Other assets		101			$ 104
Discontinued Operation, Contingent Receivable						$ 150
Forecast | Freeport-McMoRan Oil & Gas | Onshore California [Member]
Derivatives:
Discontinued Operation, Contingent Receivable, Per Year	$ 50
Crude Oil [Member] | Freeport-McMoRan Oil & Gas | Onshore California [Member]
Derivatives:
Contingent consideration, reference threshold (in us dollars per pound) | $ / bbl				70	70	70
Fair Value, Recurring [Member] | Forward Contracts [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset		$ 0