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Investments, Loans and Long-Term Receivables (Liberty Pipeline LLC (Liberty)) (Details) - USD ($) $ in Millions	Mar. 01, 2020	Mar. 31, 2020	Dec. 31, 2019
Liberty Pipeline, LLC
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest		50.00%
Maximum loss exposure		$ 216
Maximum potential amount of future payments under the guarantees		113
Variable Interest Entity, Primary Beneficiary \| Phillips 66 Partners LP
Schedule of Equity Method Investments [Line Items]
Equity investments		3,136	$ 2,961
Variable Interest Entity, Primary Beneficiary \| Phillips 66 Partners LP \| Liberty Pipeline, LLC
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest	50.00%
Payments to acquire investments	$ 75
Equity investments		$ 103