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	133						133
Net income	668				140	28	189		311
Quarterly cash distributions to unitholders and General Partner	(550)				(206)	(28)	(142)		(174)
Conversion of GP economic interest	(3)				1,381				(1,384)
Other distributions to Phillips 66	(2)				(2)
Ending Balance at Sep. 30, 2019	$ 2,754	0		(1)	$ 0	$ 746	$ 2,664		$ (655)
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)	2,470,037						2,470,037
Units issued in conversion of GP economic interest (in shares)	98,519,949				(2,480,051)				101,000,000
Ending balance, Units (in shares) at Sep. 30, 2019	241,393,883				0	13,819,791	57,813,955		169,760,137
Beginning Balance at Jun. 30, 2019	$ 2,616	0		(1)	$ (1,310)	$ 746	$ 2,555		$ 626
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common units	91						91
Net income	237					9	67		161
Quarterly cash distributions to unitholders and General Partner	(186)				(70)	(9)	(49)		(58)
Conversion of GP economic interest	(3)				1,381				(1,384)
Other distributions to Phillips 66	(1)				(1)
Ending Balance at Sep. 30, 2019	$ 2,754	0		(1)	$ 0	$ 746	$ 2,664		$ (655)
Beginning balance, Units (in shares) at Jun. 30, 2019	141,238,265				2,480,051	13,819,791	56,178,286		68,760,137
Units Outstanding [Roll Forward]
Units issued in public equity offerings (in shares)	1,635,669						1,635,669
Units issued in conversion of GP economic interest (in shares)	98,519,949				(2,480,051)				101,000,000
Ending balance, Units (in shares) at Sep. 30, 2019	241,393,883				0	13,819,791	57,813,955		169,760,137
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	697	10				29	168		490
Quarterly cash distributions to unitholders and General Partner	(627)					(28)	(153)		(446)
Transfer of equity interest	305	305
Proceeds from noncontrolling interest	3	3
Distributions to noncontrolling interest	(13)	(13)
Other distributions to Phillips 66	6								6
Ending Balance at Sep. 30, 2020	$ 3,207	305		(1)	$ 0	$ 747	$ 2,734		$ (578)
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 Sep. 30, 2020	242,159,937				0	13,819,791	58,580,009		169,760,137
Beginning Balance at Jun. 30, 2020	$ 3,213	305		(1)	$ 0	$ 746	$ 2,735		$ (572)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	216	10				10	50		146
Quarterly cash distributions to unitholders and General Partner	(209)					(9)	(51)		(149)
Proceeds from noncontrolling interest	3	3
Distributions to noncontrolling interest	(13)	(13)
Other distributions to Phillips 66	(3)								(3)
Ending Balance at Sep. 30, 2020	$ 3,207	$ 305		$ (1)	$ 0	$ 747	$ 2,734		$ (578)
Beginning balance, Units (in shares) at Jun. 30, 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 Sep. 30, 2020	242,159,937				0	13,819,791	58,580,009		169,760,137