Consolidated Statement of Changes in Equity - USD ($) $ in Millions	Total	Common Stock	Capital in Excess of Par	Treasury Stock	Retained Earnings	Accum. Other Comprehensive Loss	Noncontrolling Interests
Beginning Balance at Dec. 31, 2016	$ 23,725	$ 6	$ 19,559	$ (8,788)	$ 12,608	$ (995)	$ 1,335
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	5,248				5,106		142
Other comprehensive income (loss)	378					378
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 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
Beginning Balance, Common shares (in shares) at Dec. 31, 2016	641,594,000
Beginning Balance, Treasury stock (in shares) at Dec. 31, 2016	122,827,000
Stockholders' Equity, Shares [Roll Forward]
Shares issued—share-based compensation (in shares)	2,241,000
Repurchase of common stock (in shares)	18,738,000
Ending Balance, Common shares (in shares) at Dec. 31, 2017	643,835,000
Ending Balance, Treasury stock (in shares) at Dec. 31, 2017	141,565,000
Dividends, Common Stock [Abstract]
Dividends Paid Per Share of Common Stock (in usd per share)	$ 2.73
Net income	$ 5,873				5,595		278
Other comprehensive income (loss)	(75)					(75)
Dividends paid on common stock	(1,436)				(1,436)
Repurchase of common stock	(4,645)			(4,645)
Benefit plan activity	51		63		(12)
Issuance of Phillips 66 Partners LP common units	115		42				73
Distributions to noncontrolling interests	(207)						(207)
Ending Balance at Dec. 31, 2018	$ 27,153	6	19,873	(15,023)	20,489	(692)	2,500
Stockholders' Equity, Shares [Roll Forward]
Shares issued—share-based compensation (in shares)	1,857,000
Repurchase of common stock (in shares)	47,961,000
Ending Balance, Common shares (in shares) at Dec. 31, 2018	645,691,761
Ending Balance, Treasury stock (in shares) at Dec. 31, 2018	189,526,331
Dividends, Common Stock [Abstract]
Dividends Paid Per Share of Common Stock (in usd per share)	$ 3.10
Net income	$ 3,377				3,076		301
Other comprehensive income (loss)	(7)					(7)
Dividends paid on common stock	(1,570)				(1,570)
Repurchase of common stock	(1,650)			(1,650)
Benefit plan activity	73		85		(12)
Issuance of Phillips 66 Partners LP common units	141		68				73
Impacts from Phillips 66 Partners LP GP/IDR restructuring transaction	(98)		275				(373)
Distributions to noncontrolling interests	(241)						(241)
Ending Balance at Dec. 31, 2019	$ 27,169	$ 6	$ 20,301	$ (16,673)	$ 22,064	$ (788)	$ 2,259
Stockholders' Equity, Shares [Roll Forward]
Shares issued—share-based compensation (in shares)	1,725,000
Repurchase of common stock (in shares)	16,865,000
Ending Balance, Common shares (in shares) at Dec. 31, 2019	647,416,633
Ending Balance, Treasury stock (in shares) at Dec. 31, 2019	206,390,806
Dividends, Common Stock [Abstract]
Dividends Paid Per Share of Common Stock (in usd per share)	$ 3.50