Consolidated Statement of Changes in Equity - USD ($) $ in Millions	Total	Noncontrolling Interest	Cumulative Effect, Period of Adoption, Adjustment	Accum. Other Comprehensive Loss	General Partner	Preferred Units Public	Common Units Public	Common Units Public Cumulative Effect, Period of Adoption, Adjustment	Common Units Non-public Phillips 66
Beginning Balance at Dec. 31, 2018	$ 2,509	$ 0	$ (1)	$ (1)	$ (1,313)	$ 746	$ 2,485	$ (1)	$ 592
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common units	42						42
Net income	431				140	19	122		150
Quarterly cash distributions to unitholders and General Partner	(364)				(136)	(19)	(93)		(116)
Other contributions from Phillips 66	(1)				(1)
Ending Balance at Jun. 30, 2019	$ 2,616	0		(1)	$ (1,310)	$ 746	$ 2,555		$ 626
Beginning balance, Units (in shares) at Dec. 31, 2018	140,403,897				2,480,051	13,819,791	55,343,918		68,760,137
Units Outstanding [Roll Forward]
Units issued in public equity offerings (in shares)	834,368						834,368
Ending balance, Units (in shares) at Jun. 30, 2019	141,238,265				2,480,051	13,819,791	56,178,286		68,760,137
Beginning Balance at Mar. 31, 2019	$ 2,554	0		(1)	$ (1,315)	$ 747	$ 2,523		$ 600
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common units	10						10
Net income	233				71	9	69		84
Quarterly cash distributions to unitholders and General Partner	(184)				(69)	(10)	(47)		(58)
Other contributions from Phillips 66	3				3
Ending Balance at Jun. 30, 2019	$ 2,616	0		(1)	$ (1,310)	$ 746	$ 2,555		$ 626
Beginning balance, Units (in shares) at Mar. 31, 2019	141,025,929				2,480,051	13,819,791	55,965,950		68,760,137
Units Outstanding [Roll Forward]
Units issued in public equity offerings (in shares)	212,336						212,336
Ending balance, Units (in shares) at Jun. 30, 2019	141,238,265				2,480,051	13,819,791	56,178,286		68,760,137
Beginning Balance at Dec. 31, 2019	$ 2,834	0		(1)	$ 0	$ 746	$ 2,717		$ (628)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common units	2						2
Net income	481					19	118		344
Quarterly cash distributions to unitholders and General Partner	(418)					(19)	(102)		(297)
Transfer of equity interest	305	305
Other contributions from Phillips 66	9								9
Ending Balance at Jun. 30, 2020	$ 3,213	305		(1)	$ 0	$ 746	$ 2,735		$ (572)
Beginning balance, Units (in shares) at Dec. 31, 2019	242,119,367				0	13,819,791	58,539,439		169,760,137
Units Outstanding [Roll Forward]
Units issued in public equity offerings (in shares)	40,570						40,570
Ending balance, Units (in shares) at Jun. 30, 2020	242,159,937				0	13,819,791	58,580,009		169,760,137
Beginning Balance at Mar. 31, 2020	$ 2,853	0		(1)	$ 0	$ 747	$ 2,723		$ (616)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	255					9	63		183
Quarterly cash distributions to unitholders and General Partner	(209)				0	(10)	(51)		(148)
Transfer of equity interest	305	305
Ending Balance at Jun. 30, 2020	$ 3,213	$ 305		$ (1)	$ 0	$ 746	$ 2,735		$ (572)
Beginning balance, Units (in shares) at Mar. 31, 2020	242,159,937				0	13,819,791	58,580,009		169,760,137
Units Outstanding [Roll Forward]
Units issued in public equity offerings (in shares)	0						0
Ending balance, Units (in shares) at Jun. 30, 2020	242,159,937				0	13,819,791	58,580,009		169,760,137