Guarantees (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Environmental accruals included in recorded carrying amount	$ 442,000,000	$ 441,000,000
Gray Oak Pipeline LLC | Variable Interest Entity, Primary Beneficiary | Phillips 66 Partners LP
Guarantor Obligations [Line Items]
Maximum potential amount of future payments under the guarantees	$ 583,000,000
Effective ownership percent	42.25%
Carrying amount of indemnifications	$ 583,000,000
Other Joint Ventures
Guarantor Obligations [Line Items]
Joint venture debt obligations, period (up to)	P8Y
Other Guarantees | Other Joint Ventures
Guarantor Obligations [Line Items]
Maximum potential amount of future payments under the guarantees	$ 331,000,000
Indemnifications
Guarantor Obligations [Line Items]
Carrying amount of indemnifications	159,000,000	153,000,000
Indemnifications | Asset Retirement Obligations And Accrued Environmental Cost
Guarantor Obligations [Line Items]
Environmental accruals included in recorded carrying amount	111,000,000	$ 105,000,000
Facilities | Residual Value Guarantees
Guarantor Obligations [Line Items]
Maximum potential amount of future payments under the guarantees	554,000,000
Railcar and Airplane | Residual Value Guarantees
Guarantor Obligations [Line Items]
Maximum potential amount of future payments under the guarantees	$ 362,000,000
Lessee leasing arrangements, operating leases, term of contract (up to)	4 years