Fair Value Measurement (Unobservable inputs) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Other Assets, Current	$ 419	$ 655
Other Assets, Noncurrent	1,654	1,885
Gulf of Mexico Contingent Consideration [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(9)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value at January 1, 2020	108
Net unrealized loss related to assets still held at the end of the period	(15)
Fair value at September 30, 2020	84
Onshore California [Member] | Freeport-McMoRan Oil & Gas
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent Receivable			$ 150
Other Assets, Noncurrent	$ 0	$ 11