Segment Disclosures and Related Information (Summary of Sales and Other Operating Revenues, Net Income (Loss) Attributable to Phillips 66 and Total Assets by Operating Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Sales and other operating revenues	$ 20,878	$ 23,103
Consolidated income (loss) before income taxes	(2,478)	340
Total Assets	53,460		$ 58,720
Midstream
Segment Reporting Information [Line Items]
Sales and other operating revenues	1,043	1,313
Refining
Segment Reporting Information [Line Items]
Sales and other operating revenues	6,148	7,093
Marketing and Specialties
Segment Reporting Information [Line Items]
Sales and other operating revenues	13,679	14,689
Operating Segments | Midstream
Segment Reporting Information [Line Items]
Sales and other operating revenues	1,538	1,897
Consolidated income (loss) before income taxes	(702)	316
Total Assets	14,846		15,716
Operating Segments | Chemicals
Segment Reporting Information [Line Items]
Sales and other operating revenues	1	1
Consolidated income (loss) before income taxes	169	227
Total Assets	6,376		6,249
Operating Segments | Refining
Segment Reporting Information [Line Items]
Sales and other operating revenues	13,781	16,861
Consolidated income (loss) before income taxes	(2,261)	(198)
Total Assets	22,516		25,150
Operating Segments | Marketing and Specialties
Segment Reporting Information [Line Items]
Sales and other operating revenues	14,249	15,242
Consolidated income (loss) before income taxes	513	205
Total Assets	7,108		8,659
Intersegment eliminations | Midstream
Segment Reporting Information [Line Items]
Sales and other operating revenues	(495)	(584)
Intersegment eliminations | Refining
Segment Reporting Information [Line Items]
Sales and other operating revenues	(7,633)	(9,768)
Intersegment eliminations | Marketing and Specialties
Segment Reporting Information [Line Items]
Sales and other operating revenues	(570)	(553)
Corporate and Other
Segment Reporting Information [Line Items]
Sales and other operating revenues	7	7
Consolidated income (loss) before income taxes	(197)	$ (210)
Total Assets	$ 2,614		$ 2,946