Consolidated Statement of Changes in Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock	Capital in Excess of Par	Treasury Stock	Treasury Stock Repurchase Plan	Retained Earnings	Accum. Other Comprehensive Loss	Noncontrolling Interests
Beginning Balance at Dec. 31, 2014	$ 22,037	$ 6	$ 19,040	$ (6,234)		$ 9,309	$ (531)	$ 447
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	4,280					4,227		53
Other comprehensive income (loss)	(122)						(122)
Cash dividends paid on common stock	(1,172)					(1,172)
Repurchase of common stock	(1,512)			(1,512)
Benefit plan activity	89		105			(16)
Issuance of Phillips 66 Partners LP common and preferred units	384							384
Distributions to noncontrolling interests	(46)							(46)
Ending Balance at Dec. 31, 2015	$ 23,938	6	19,145	(7,746)		12,348	(653)	838
Beginning Balance, Common shares (in shares) at Dec. 31, 2014	637,032
Beginning Balance, Treasury shares (in shares) at Dec. 31, 2014					90,650
Shares
Shares issued—share-based compensation (in shares)	2,304
Repurchase of common stock (in shares)					19,276
Ending Balance, Common shares (in shares) at Dec. 31, 2015	639,336
Ending Balance, Treasury shares (in shares) at Dec. 31, 2015					109,926
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	$ 1,644					1,555		89
Other comprehensive income (loss)	(342)						(342)
Cash dividends paid on common stock	(1,282)					(1,282)
Repurchase of common stock	(1,042)			(1,042)
Benefit plan activity	93		106			(13)
Issuance of Phillips 66 Partners LP common and preferred units	791		308					483
Distributions to noncontrolling interests	(75)							(75)
Ending Balance at Dec. 31, 2016	$ 23,725	6	19,559	(8,788)		12,608	(995)	1,335
Shares
Shares issued—share-based compensation (in shares)	2,258
Repurchase of common stock (in shares)					12,901
Ending Balance, Common shares (in shares) at Dec. 31, 2016	641,594
Ending Balance, Treasury shares (in shares) at Dec. 31, 2016					122,827
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	$ 5,248					5,106		142
Other comprehensive income (loss)	378						378
Cash dividends paid on common stock	(1,395)					(1,395)
Repurchase of common stock	(1,590)			(1,590)
Benefit plan activity	59		72			(13)
Issuance of Phillips 66 Partners LP common and preferred units	1,123		137					986
Distributions to noncontrolling interests	(120)							(120)
Ending Balance at Dec. 31, 2017	$ 27,428	$ 6	$ 19,768	$ (10,378)		$ 16,306	$ (617)	$ 2,343
Shares
Shares issued—share-based compensation (in shares)	2,241
Repurchase of common stock (in shares)					18,738
Ending Balance, Common shares (in shares) at Dec. 31, 2017	643,835
Ending Balance, Treasury shares (in shares) at Dec. 31, 2017					141,565