Fair Value Measurement (Fair Value Measurement Inputs) (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 $ / bbl	Dec. 31, 2016 USD ($) $ / bbl
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Other Assets, Current	$ 795			$ 655
Other assets	1,691			1,885
Proceeds from Sale of Other Assets, contingent consideration	66	$ 84
Derivative Liability, Fair Value, Gross Liability	147			21
Investment securities (current and long-term):
Marketable Securities	0
Derivatives:
Derivative Asset	36			74
Derivatives: [Abstract]
Derivative Liability	145			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	28			27
Trust Assets Fair Value Disclosure	60			59
Derivatives:
Derivative Asset	0			0
Derivatives: [Abstract]
Derivative Liability	0			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	3			4
Trust Assets Fair Value Disclosure	8			3
Derivatives:
Derivative Asset	1			5
Derivatives: [Abstract]
Derivative Liability	(25)			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	132			134
Derivatives:
Derivative Asset	37			80
Derivatives: [Abstract]
Derivative Liability	(122)			21
Long-term debt, including current portion	9,530			10,239
Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Discontinued Operation, Contingent Receivable	78			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			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	78			108
Investment securities (current and long-term):
Investments, Fair Value Disclosure	31			31
Trust Assets Fair Value Disclosure	200			196
Derivatives:
Derivative Asset	38			85
Derivatives: [Abstract]
Derivative Liability	(147)			21
Long-term debt, including current portion	9,530			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	119			122
Investment securities (current and long-term):
Investments, Fair Value Disclosure	31			31
Trust Assets Fair Value Disclosure	200			196
Derivatives:
Derivative Asset	38			85
Derivatives: [Abstract]
Derivative Liability	(147)			21
Long-term debt, including current portion	10,074			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	119			20
Derivatives:
Derivative Asset	33			68
Derivatives: [Abstract]
Derivative Liability	118			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	34			68
Derivatives: [Abstract]
Derivative Liability	(119)			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	34			68
Derivatives: [Abstract]
Derivative Liability	(119)			20
Embedded Derivative Financial Instruments [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset	34			68
Derivatives: [Abstract]
Derivative Liability	(119)			20
Forward Contracts [Member] | Level 1
Derivatives:
Derivative Asset	1
Forward Contracts [Member] | Level 2
Derivatives:
Derivative Asset	3
Forward Contracts [Member] | Level 3
Derivatives:
Derivative Asset	0
Forward Contracts [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset	4
Forward Contracts [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset	4
Commodity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivative Liability, Fair Value, Gross Liability	28			1
Derivatives:
Derivative Asset	3			6
Derivatives: [Abstract]
Derivative Liability	27			1
Commodity Contract [Member] | Fair Value Measured at Net Asset Value Per Share [Member]
Derivatives: [Abstract]
Derivative Liability	0			0
Commodity Contract [Member] | Level 1
Derivatives:
Derivative Asset				5
Derivatives: [Abstract]
Derivative Liability	(25)			0
Commodity Contract [Member] | Level 2
Derivatives:
Derivative Asset				1
Derivatives: [Abstract]
Derivative Liability	(3)			1
Commodity Contract [Member] | Level 3
Derivatives:
Derivative Asset				0
Derivatives: [Abstract]
Derivative Liability	0			0
Commodity Contract [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset				6
Derivatives: [Abstract]
Derivative Liability	(28)			1
Commodity Contract [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset				6
Derivatives: [Abstract]
Derivative Liability	(28)			1
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	28			27
Trust Assets Fair Value Disclosure	60			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	28			27
Trust Assets Fair Value Disclosure	60			59
U.S. core fixed income fund [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Marketable Securities	28			27
Trust Assets Fair Value Disclosure	60			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	3			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	3			4
Equity securities | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Marketable Securities	3			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	22			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	22			36
Government bonds | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	22			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	39			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	39			33
Corporate bonds [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	39			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	55			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	55			43
Government mortgage-backed securities [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	55			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	11			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	11			14
Asset-backed securities [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	11			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	8			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	8			3
Money market funds [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	8			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	113			100
Other assets	151			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	119			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	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
Fair Value, Recurring [Member] | Forward Contracts [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset	$ 0