Earnings (Loss) Per Share - Summary of Earnings Per Share Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Basic
Net income (loss) attributable to Phillips 66	$ 582	$ (654)
Income allocated to participating securities	(2)	(2)
Net income (loss) available to common stockholders	$ 580	$ (656)
Weighted-average common shares outstanding (in shares)	447,206	437,369
Effect of share-based compensation (in shares)	2,092	2,135
Weighted-average commons shares outstanding - EPS (in shares)	449,298	439,504
Earnings (Loss) Per Share of Common Stock (in usd per share)	$ 1.29	$ (1.49)
Diluted
Net income (loss) attributable to Phillips 66	$ 582	$ (654)
Income allocated to participating securities	(2)	(2)
Net income (loss) available to common stockholders	$ 580	$ (656)
Weighted-average common shares outstanding (in shares)	449,298	439,504
Effect of share-based compensation (in shares)	713	0
Weighted-average commons shares outstanding - EPS (in shares)	450,011	439,504
Earnings (Loss) Per Share of Common Stock (in usd per share)	$ 1.29	$ (1.49)