Investments, Loans and Long-Term Receivables - Dakota Access, LLC and Energy Transfer Crude Oil, Company, LLC (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2019
Dakota Access, LLC | Forecast
Schedule of Equity Method Investments [Line Items]
Scheduled interest payments annually	$ 25,000,000
Phillips 66 Partners LP | Variable Interest Entity, Primary Beneficiary
Schedule of Equity Method Investments [Line Items]
Equity investments		$ 3,029,000,000	$ 3,244,000,000
Phillips 66 Partners LP | Variable Interest Entity, Primary Beneficiary | Dakota Access and ETCO
Schedule of Equity Method Investments [Line Items]
Maximum exposure, undiscounted		631,000,000
Equity investments		$ 575,000,000
Senior Notes | Dakota Access, LLC
Schedule of Equity Method Investments [Line Items]
Debt issued and guaranteed				$ 2,500,000,000