Fair Value Measurement (Fair Value Measurement Inputs) (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) $ / bbl	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2016 USD ($) $ / bbl	Nov. 16, 2016 USD ($) $ / lb
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Other Assets, Current	$ 560		$ 422
Other assets	2,174		2,172
Proceeds from Sale of Other Assets, contingent consideration	84	$ 0
Assets	41,059	$ 36,637	42,216
Derivative Liability, Fair Value, Gross Liability	15		48
Derivatives:
Derivative Asset	93		16
Derivatives: [Abstract]
Derivative Liability	13		41
Fair Value Measured at Net Asset Value Per Share [Member]
Investment securities (current and long-term):
Investments, Fair Value Disclosure	25		25
Trust Assets Fair Value Disclosure	57		55
Level 1
Investment securities (current and long-term):
Investments, Fair Value Disclosure	4		4
Trust Assets Fair Value Disclosure	6		5
Derivatives:
Derivative Asset	8		0
Contingent Receivable	0		0
Derivatives: [Abstract]
Derivative Liability	0		7
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	123		121
Derivatives:
Derivative Asset	174		96
Contingent Receivable	0		0
Derivatives: [Abstract]
Derivative Liability	15		41
Long-term debt, including current portion	9,659		10,238
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
Contingent Receivable	117		127
Derivatives: [Abstract]
Derivative Liability	0		0
Long-term debt, including current portion	0		0
Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Investments, Fair Value Disclosure	29		29
Trust Assets Fair Value Disclosure	186		181
Derivatives:
Derivative Asset	182		96
Contingent Receivable	117		127
Derivatives: [Abstract]
Derivative Liability	15		48
Long-term debt, including current portion	9,659		10,238
Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Investments, Fair Value Disclosure	29		29
Trust Assets Fair Value Disclosure	186		181
Derivatives:
Derivative Asset	182		96
Contingent Receivable	138		143
Derivatives: [Abstract]
Derivative Liability	15		48
Long-term debt, including current portion	9,905		11,141
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	14		39
Derivatives:
Derivative Asset	84		16
Derivatives: [Abstract]
Derivative Liability	13		32
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	85		23
Derivatives: [Abstract]
Derivative Liability	14		39
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	85		23
Derivatives: [Abstract]
Derivative Liability	14		39
Embedded Derivative Financial Instruments [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset	85		23
Derivatives: [Abstract]
Derivative Liability	14		39
Forward Contracts [Member] | Level 1
Derivatives:
Derivative Asset	0
Forward Contracts [Member] | Level 2
Derivatives:
Derivative Asset	1
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	1		9
Derivatives:
Derivative Asset	9		0
Derivatives: [Abstract]
Derivative Liability	0		9
Commodity Contract [Member] | Level 1
Derivatives: [Abstract]
Derivative Liability	0		7
Commodity Contract [Member] | Level 2
Derivatives: [Abstract]
Derivative Liability	1		2
Commodity Contract [Member] | Level 3
Derivatives: [Abstract]
Derivative Liability	0		0
Commodity Contract [Member] | Estimate of Fair Value Measurement [Member]
Derivatives: [Abstract]
Derivative Liability	1		9
Commodity Contract [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives: [Abstract]
Derivative Liability	1		9
Future [Member] | Level 1
Derivatives:
Derivative Asset	8
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	9
Future [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset	9
Africa and onshore California [Member] | Commodity Contract [Member] | Level 1
Derivatives:
Derivative Asset	0		0
Africa and onshore California [Member] | Commodity Contract [Member] | Level 2
Derivatives:
Derivative Asset	87		73
Africa and onshore California [Member] | Commodity Contract [Member] | Level 3
Derivatives:
Derivative Asset	0		0
Africa and onshore California [Member] | Commodity Contract [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset	87		73
Africa and onshore California [Member] | Commodity Contract [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset	87		73
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	25		25
Trust Assets Fair Value Disclosure	57		55
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	25		25
Trust Assets Fair Value Disclosure	57		55
U.S. core fixed income fund [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Marketable Securities	25		25
Trust Assets Fair Value Disclosure	57		55
Equity securities | Level 1
Investment securities (current and long-term):
Marketable Securities	4		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	4		4
Equity securities | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Marketable Securities	4		4
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	33		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	33		36
Government bonds | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	33		36
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	29		28
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	29		28
Corporate bonds [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	29		28
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	41		38
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	41		38
Government mortgage-backed securities [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	41		38
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	12		11
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	12		11
Asset-backed securities [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	12		11
Money market funds [Member] | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	6		5
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	6		5
Money market funds [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	6		5
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	7		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	7		7
Collateralized Mortgage Backed Securities [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	7		7
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	115		109
Other assets	163		126
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	14		39
TF Holdings Limited | Discontinued Operations, Disposed of by Sale
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Other assets	58		57
Derivatives:
Contingent Receivable							$ 120
Copper | TF Holdings Limited | Discontinued Operations, Disposed of by Sale
Derivatives:
Contingent Receivable							60
Cobalt | TF Holdings Limited | Discontinued Operations, Disposed of by Sale
Derivatives:
Contingent Receivable							$ 60
Contingent consideration, reference threshold (in us dollars per pound) | $ / lb							20
Freeport-McMoRan Oil & Gas | Onshore California [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Other Assets, Current	13
Other assets	16		16
Proceeds from Sale of Other Assets, contingent consideration	50
Assets	29
Derivatives:
Contingent Receivable	150
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	19		27
Other assets	$ 119		$ 116
Derivatives:
Contingent Receivable						$ 150
Scenario, Forecast [Member] | Freeport-McMoRan Oil & Gas | Onshore California [Member]
Derivatives:
Contingent Receivable				$ 50	$ 50
Crude Oil [Member] | Freeport-McMoRan Oil & Gas | Onshore California [Member]
Derivatives:
Contingent consideration, reference threshold (in us dollars per pound) | $ / bbl			70			70
Maximum [Member] | Copper | TF Holdings Limited | Discontinued Operations, Disposed of by Sale
Derivatives:
Contingent consideration, reference threshold (in us dollars per pound) | $ / lb							3.50