Sweeny Fractionator Acquisition (Narrative) (Details) $ in Millions			1 Months Ended		3 Months Ended
	Mar. 01, 2016 USD ($) shares	Dec. 01, 2015	Mar. 31, 2016 USD ($) bbl / d shares	Mar. 31, 2015	Mar. 31, 2016 USD ($) bbl / d shares	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) shares
Business Acquisition [Line Items]
General partner interest, percent	2.00%	2.00%	2.00%	2.00%
Processing capacity, in barrels per day | bbl / d			100,000		100,000
Number of general partner units owned by Phillips 66 | shares			1,691,850		1,691,850		1,683,425
Net properties, plants and equipment			$ 1,641.5		$ 1,641.5		$ 1,625.2	[1]
Phillips 66 [Member]
Business Acquisition [Line Items]
Number of general partner units owned by Phillips 66 | shares			1,691,850		1,691,850
Phillips 66 [Member] | Phillips 66 [Member]
Business Acquisition [Line Items]
Limited partner ownership interest, percent			69.50%
Phillips 66 [Member] | Phillips 66 [Member] | Common Units [Member]
Business Acquisition [Line Items]
Number of units owned by Phillips 66 | shares			58,761,865		58,761,865
Sweeny Fractionator Acquisition [Member]
Business Acquisition [Line Items]
Units issued associated with acquisition | shares					421,248
Sweeny Fractionator Acquisition [Member] | Phillips 66 [Member] | General Partner Units [Member]
Business Acquisition [Line Items]
Units issued associated with acquisition | shares	8,425
Sweeny Fractionator Acquisition [Member] | Phillips 66 [Member] | Phillips 66 [Member]
Business Acquisition [Line Items]
Controlling interest acquired, percentage	25.00%
Total consideration	$ 236.0
Assumption of a note payable to a subsidiary of Phillips 66	212.0
Transaction costs	0.9
Net book value of interest acquired	$ 283.0
Sweeny Fractionator Acquisition [Member] | Phillips 66 [Member] | Phillips 66 [Member] | Common Units [Member]
Business Acquisition [Line Items]
Units issued associated with acquisition | shares	412,823
Phillips 66 Sweeny Frac LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Business Acquisition [Line Items]
Net properties, plants and equipment			$ 1,151.4		$ 1,151.4
Net Income (Loss) Attributable To Predecessors [Member] | Phillips 66 Sweeny Frac LLC [Member]
Business Acquisition [Line Items]
Earnings (loss) attributable to noncontrolling interest					$ 3.7	$ (2.0)
Net investment Predecessors [Member] | Phillips 66 Sweeny Frac LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Business Acquisition [Line Items]
Noncontrolling interests							$ 800.2

[1] Prior-period financial information has been retrospectively adjusted for acquisitions of businesses under common control.