Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected Quarterly Financial Information [Abstract]
Sales and Other Operating Revenues	$ 29,125	$ 27,218	$ 27,847	$ 23,103	$ 29,098	$ 29,788	$ 28,980	$ 23,595	$ 107,293	$ 111,461
Income Before Income Taxes	1,066	943	1,829	340	2,918	1,975	1,835	717	4,178	7,445	$ 3,555
Net Income	810	793	1,504	270	2,316	1,568	1,404	585	3,377	5,873	5,248
Net Income Attributable to Phillips 66	$ 736	$ 712	$ 1,424	$ 204	$ 2,240	$ 1,492	$ 1,339	$ 524	$ 3,076	$ 5,595	$ 5,106
Basic (in dollars per share)	$ 1.65	$ 1.58	$ 3.13	$ 0.44	$ 4.85	$ 3.20	$ 2.86	$ 1.07	$ 6.80	$ 11.87	$ 9.90
Diluted (in dollars per share)	$ 1.64	$ 1.58	$ 3.12	$ 0.44	$ 4.82	$ 3.18	$ 2.84	$ 1.07	$ 6.77	$ 11.80	$ 9.85