Condensed Consolidating Financial Information (Cash Flow) (Details) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
		Feb. 28, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows From Operating Activities
Net Cash Provided by Operating Activities			$ 4,808	$ 7,573	$ 3,648
Cash Flows From Investing Activities
Capital expenditures and investments			(3,873)	(2,639)	(1,832)
Proceeds from asset dispositions	[1]		157	57	86
Intercompany lending activities			0	0	0
Advances/loans—related parties			(98)	(1)	(10)
Collection of advances/loans—related parties			95	0	326
Restricted cash from consolidation of business					318
Other			31	112	(34)
Net Cash Provided by (Used in) Investing Activities			(3,688)	(2,471)	(1,146)
Cash Flows From Financing Activities
Issuance of debt			1,783	2,184	3,508
Repayment of debt			(1,307)	(1,144)	(3,678)
Issuance of common stock			32	39	35
Repurchase of common stock		$ (3,280)	(1,650)	(4,645)	(1,590)
Dividends paid on common stock			(1,570)	(1,436)	(1,395)
Distributions to noncontrolling interests			(241)	(207)	(120)
Net proceeds from issuance of Phillips 66 Partners LP common and preferred units			173	128	1,205
Other			269	(86)	(76)
Net Cash Provided by (Used in) Financing Activities			(2,511)	(5,167)	(2,111)
Effect of Exchange Rate Changes on Cash and Cash Equivalents			(14)	(35)	17
Net Change in Cash, Cash Equivalents and Restricted Cash			(1,405)	(100)	408
Cash, cash equivalents and restricted cash at beginning of year			3,019	3,119	2,711
Cash, Cash Equivalents and Restricted Cash at End of Year			1,614	3,019	3,119
Consolidating Adjustments
Cash Flows From Operating Activities
Net Cash Provided by Operating Activities			(3,954)	(4,986)	(3,420)
Cash Flows From Investing Activities
Capital expenditures and investments			260	0	140
Proceeds from asset dispositions			(350)	(455)	(263)
Intercompany lending activities			0	0	0
Advances/loans—related parties			0	0	0
Collection of advances/loans—related parties			0		0
Restricted cash from consolidation of business					0
Other			0	0	0
Net Cash Provided by (Used in) Investing Activities			(90)	(455)	(123)
Cash Flows From Financing Activities
Issuance of debt			0	0	0
Repayment of debt			0	0	0
Issuance of common stock			0	0	0
Repurchase of common stock			0	0	0
Dividends paid on common stock			3,954	4,986	3,420
Distributions to noncontrolling interests			0	0	0
Net proceeds from issuance of Phillips 66 Partners LP common and preferred units			0	0	0
Other			90	455	123
Net Cash Provided by (Used in) Financing Activities			4,044	5,441	3,543
Effect of Exchange Rate Changes on Cash and Cash Equivalents			0	0	0
Net Change in Cash, Cash Equivalents and Restricted Cash			0	0	0
Cash, cash equivalents and restricted cash at beginning of year			0	0	0
Cash, Cash Equivalents and Restricted Cash at End of Year			0	0	0
Phillips 66 | Reportable Legal Entities
Cash Flows From Operating Activities
Net Cash Provided by Operating Activities			3,541	2,955	2,619
Cash Flows From Investing Activities
Capital expenditures and investments			0	0	0
Proceeds from asset dispositions			0	0	0
Intercompany lending activities			(297)	2,214	401
Advances/loans—related parties			0	0	0
Collection of advances/loans—related parties			0		0
Restricted cash from consolidation of business					0
Other			0	0	0
Net Cash Provided by (Used in) Investing Activities			(297)	2,214	401
Cash Flows From Financing Activities
Issuance of debt			0	1,509	1,500
Repayment of debt			0	(550)	(1,500)
Issuance of common stock			32	39	35
Repurchase of common stock			(1,650)	(4,645)	(1,590)
Dividends paid on common stock			(1,570)	(1,436)	(1,395)
Distributions to noncontrolling interests			0	0	0
Net proceeds from issuance of Phillips 66 Partners LP common and preferred units			0	0	0
Other			(56)	(86)	(70)
Net Cash Provided by (Used in) Financing Activities			(3,244)	(5,169)	(3,020)
Effect of Exchange Rate Changes on Cash and Cash Equivalents			0	0	0
Net Change in Cash, Cash Equivalents and Restricted Cash			0	0	0
Cash, cash equivalents and restricted cash at beginning of year			0	0	0
Cash, Cash Equivalents and Restricted Cash at End of Year			0	0	0
Phillips 66 Company | Reportable Legal Entities
Cash Flows From Operating Activities
Net Cash Provided by Operating Activities			2,923	6,962	2,702
Cash Flows From Investing Activities
Capital expenditures and investments			(1,493)	(998)	(1,133)
Proceeds from asset dispositions			354	462	265
Intercompany lending activities			567	(3,031)	1,453
Advances/loans—related parties			0	0	(10)
Collection of advances/loans—related parties			0		75
Restricted cash from consolidation of business					0
Other			(8)	27	(26)
Net Cash Provided by (Used in) Investing Activities			(580)	(3,540)	624
Cash Flows From Financing Activities
Issuance of debt			0	0	0
Repayment of debt			(15)	(11)	(17)
Issuance of common stock			0	0	0
Repurchase of common stock			0	0	0
Dividends paid on common stock			(3,836)	(3,174)	(2,752)
Distributions to noncontrolling interests			0	0	0
Net proceeds from issuance of Phillips 66 Partners LP common and preferred units			0	0	0
Other			(4)	0	0
Net Cash Provided by (Used in) Financing Activities			(3,855)	(3,185)	(2,769)
Effect of Exchange Rate Changes on Cash and Cash Equivalents			0	0	0
Net Change in Cash, Cash Equivalents and Restricted Cash			(1,512)	237	557
Cash, cash equivalents and restricted cash at beginning of year			1,648	1,411	854
Cash, Cash Equivalents and Restricted Cash at End of Year			136	1,648	1,411
All Other Subsidiaries | Reportable Legal Entities
Cash Flows From Operating Activities
Net Cash Provided by Operating Activities			2,298	2,642	1,747
Cash Flows From Investing Activities
Capital expenditures and investments			(2,640)	(1,641)	(839)
Proceeds from asset dispositions			153	50	84
Intercompany lending activities			(270)	817	(1,854)
Advances/loans—related parties			(98)	(1)	0
Collection of advances/loans—related parties			95		251
Restricted cash from consolidation of business					318
Other			39	85	(8)
Net Cash Provided by (Used in) Investing Activities			(2,721)	(690)	(2,048)
Cash Flows From Financing Activities
Issuance of debt			1,783	675	2,008
Repayment of debt			(1,292)	(583)	(2,161)
Issuance of common stock			0	0	0
Repurchase of common stock			0	0	0
Dividends paid on common stock			(118)	(1,812)	(668)
Distributions to noncontrolling interests			(241)	(207)	(120)
Net proceeds from issuance of Phillips 66 Partners LP common and preferred units			173	128	1,205
Other			239	(455)	(129)
Net Cash Provided by (Used in) Financing Activities			544	(2,254)	135
Effect of Exchange Rate Changes on Cash and Cash Equivalents			(14)	(35)	17
Net Change in Cash, Cash Equivalents and Restricted Cash			107	(337)	(149)
Cash, cash equivalents and restricted cash at beginning of year			1,371	1,708	1,857
Cash, Cash Equivalents and Restricted Cash at End of Year			$ 1,478	$ 1,371	$ 1,708

[1] Includes return of investments in equity affiliates.