Derivatives and Financial Instruments (Summary of Outstanding Commodity Derivative Contracts) (Details) - MMBbls MMBbls in Millions	Dec. 31, 2019	Dec. 31, 2018
Commodity
Crude oil, refined petroleum products and NGL (millions of barrels)	(16)	(17)

Non Monetary Notional Amount Of Price Risk Derivative Instruments Not Designated As Hedging Instruments, Net

No definition available.

Name:	psx_NonMonetaryNotionalAmountOfPriceRiskDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsNet
Namespace Prefix:	psx_
Data Type:	num:volumeItemType
Balance Type:	na
Period Type:	instant