Condensed Consolidating Financial Information (Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash Flows From Operating Activities
Net Cash Provided by (Used in) Operating Activities	$ 217	$ (478)
Cash Flows From Investing Activities
Capital expenditures and investments	(923)	(1,097)
Return of investments in equity affiliates	38	21
Proceeds from asset dispositions	1	82
Intercompany lending activities	0	0
Advances/loans—related parties	(8)	0
Other	15	(18)
Net Cash Used in Investing Activities	(877)	(1,012)
Cash Flows From Financing Activities
Issuance of debt	1,199	725
Repayment of debt	(7)	(592)
Issuance of common stock	6	8
Repurchase of common stock	(443)	(344)
Dividends paid on common stock	(396)	(364)
Distributions to noncontrolling interests	(61)	(56)
Net proceeds from issuance of Phillips 66 Partners LP common units	2	32
Other	(24)	307
Net Cash Provided by (Used in) Financing Activities	276	(284)
Effect of Exchange Rate Changes on Cash and Cash Equivalents	(9)	8
Net Change in Cash and Cash Equivalents	(393)	(1,766)
Cash and cash equivalents at beginning of period	1,614	3,019
Cash and Cash Equivalents at End of Period	1,221	1,253
Reportable Legal Entities | Phillips 66
Cash Flows From Operating Activities
Net Cash Provided by (Used in) Operating Activities	643	3
Cash Flows From Investing Activities
Capital expenditures and investments	0	0
Return of investments in equity affiliates	0	0
Proceeds from asset dispositions	0	0
Intercompany lending activities	(973)	731
Advances/loans—related parties	0
Other	0	0
Net Cash Used in Investing Activities	(973)	731
Cash Flows From Financing Activities
Issuance of debt	1,199	0
Repayment of debt	0	0
Issuance of common stock	6	8
Repurchase of common stock	(443)	(344)
Dividends paid on common stock	(396)	(364)
Distributions to noncontrolling interests	0	0
Net proceeds from issuance of Phillips 66 Partners LP common units	0	0
Other	(36)	(34)
Net Cash Provided by (Used in) Financing Activities	330	(734)
Effect of Exchange Rate Changes on Cash and Cash Equivalents	0	0
Net Change in Cash and Cash Equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and Cash Equivalents at End of Period	0	0
Reportable Legal Entities | Phillips 66 Company
Cash Flows From Operating Activities
Net Cash Provided by (Used in) Operating Activities	(364)	(384)
Cash Flows From Investing Activities
Capital expenditures and investments	(292)	(234)
Return of investments in equity affiliates	0	0
Proceeds from asset dispositions	1	0
Intercompany lending activities	1,914	(806)
Advances/loans—related parties	0
Other	(25)	(26)
Net Cash Used in Investing Activities	1,598	(1,066)
Cash Flows From Financing Activities
Issuance of debt	0	0
Repayment of debt	(5)	(5)
Issuance of common stock	0	0
Repurchase of common stock	0	0
Dividends paid on common stock	(556)
Distributions to noncontrolling interests	0	0
Net proceeds from issuance of Phillips 66 Partners LP common units	0	0
Other	0	0
Net Cash Provided by (Used in) Financing Activities	(561)	(5)
Effect of Exchange Rate Changes on Cash and Cash Equivalents	0	0
Net Change in Cash and Cash Equivalents	673	(1,455)
Cash and cash equivalents at beginning of period	136	1,648
Cash and Cash Equivalents at End of Period	809	193
Reportable Legal Entities | All Other Subsidiaries
Cash Flows From Operating Activities
Net Cash Provided by (Used in) Operating Activities	494	21
Cash Flows From Investing Activities
Capital expenditures and investments	(631)	(863)
Return of investments in equity affiliates	38	21
Proceeds from asset dispositions	0	82
Intercompany lending activities	(941)	75
Advances/loans—related parties	(8)
Other	40	8
Net Cash Used in Investing Activities	(1,502)	(677)
Cash Flows From Financing Activities
Issuance of debt	0	725
Repayment of debt	(2)	(587)
Issuance of common stock	0	0
Repurchase of common stock	0	0
Dividends paid on common stock	0	(118)
Distributions to noncontrolling interests	(61)	(56)
Net proceeds from issuance of Phillips 66 Partners LP common units	2	32
Other	12	341
Net Cash Provided by (Used in) Financing Activities	(49)	337
Effect of Exchange Rate Changes on Cash and Cash Equivalents	(9)	8
Net Change in Cash and Cash Equivalents	(1,066)	(311)
Cash and cash equivalents at beginning of period	1,478	1,371
Cash and Cash Equivalents at End of Period	412	1,060
Consolidating Adjustments
Cash Flows From Operating Activities
Net Cash Provided by (Used in) Operating Activities	(556)	(118)
Cash Flows From Investing Activities
Capital expenditures and investments	0	0
Return of investments in equity affiliates	0	0
Proceeds from asset dispositions	0	0
Intercompany lending activities	0	0
Advances/loans—related parties	0
Other	0	0
Net Cash Used in Investing Activities	0	0
Cash Flows From Financing Activities
Issuance of debt	0	0
Repayment of debt	0	0
Issuance of common stock	0	0
Repurchase of common stock	0	0
Dividends paid on common stock	556	118
Distributions to noncontrolling interests	0	0
Net proceeds from issuance of Phillips 66 Partners LP common units	0	0
Other	0	0
Net Cash Provided by (Used in) Financing Activities	556	118
Effect of Exchange Rate Changes on Cash and Cash Equivalents	0	0
Net Change in Cash and Cash Equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and Cash Equivalents at End of Period	$ 0	$ 0