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, 2020	Mar. 31, 2019
Basic
Net income (loss) attributable to Phillips 66	$ (2,496)	$ 204
Income allocated to participating securities	(1)	(1)
Net income (loss) available to common stockholders	$ (2,497)	$ 203
Weighted-average common shares outstanding (in shares)	439,014	454,886
Effect of share-based compensation (in shares)	2,331	2,713
Weighted-average commons shares outstanding - EPS (in shares)	441,345	457,599
Earnings (Loss) Per Share of Common Stock (in usd per share)	$ (5.66)	$ 0.44
Diluted
Net income (loss) attributable to Phillips 66	$ (2,496)	$ 204
Income allocated to participating securities	(1)	(1)
Net income (loss) available to common stockholders	$ (2,497)	$ 203
Weighted-average common shares outstanding (in shares)	441,345	457,599
Effect of share-based compensation (in shares)	0	1,690
Weighted-average commons shares outstanding - EPS (in shares)	441,345	459,289
Earnings (Loss) Per Share of Common Stock (in usd per share)	$ (5.66)	$ 0.44

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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Amount after tax of income (loss) from continuing operations attributable to the parent.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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