Fractionator Acquisitions (Schedule of Results of Operations Giving Effect to Acquisitions) (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015		Sep. 30, 2016	Sep. 30, 2015
Revenues and Other Income
Operating revenues—related parties	$ 108.4	$ 71.1	[1]	$ 315.7	$ 204.0	[1]
Operating revenues—third parties	1.8	0.7	[1]	5.9	2.7	[1]
Equity in earnings of affiliates	33.8	25.2	[1]	88.5	51.9	[1]
Other income	0.3	0.1	[1]	0.8	0.2	[1]
Revenues And Other Income	144.3	97.1	[1]	410.9	258.8	[1]
Costs and Expenses
Operating and maintenance expenses	25.5	20.3	[1]	76.4	56.3	[1]
Depreciation	15.1	6.1	[1]	43.5	16.8	[1]
General and administrative expenses	9.2	7.4	[1]	26.0	23.2	[1]
Taxes other than income taxes	1.2	3.1	[1]	12.3	8.9	[1]
Interest and debt expense	9.9	9.2	[1]	30.8	24.6	[1]
Other expenses	0.1			0.1	0.1	[1]
Total costs and expenses	61.0	46.1	[1]	189.1	129.9	[1]
Income before income taxes	83.3	51.0	[1]	221.8	128.9	[1]
Provision for income taxes	0.2	0.1		0.8	0.2
Net Income	83.1	50.9	[1]	221.0	128.7	[1]
Less: Net income attributable to noncontrolling interests				0.0
Less: Net income (loss) attributable to Predecessors		(1.4)	[1]	18.1	(1.0)	[1]
Net income attributable to the Partnership	$ 83.1	52.3	[1]	202.9	129.7	[1]
Phillips 66 Partners LP (As Previously Reported) [Member]
Revenues and Other Income
Operating revenues—related parties		65.4		291.4	190.5
Operating revenues—third parties		0.7		5.9	2.7
Equity in earnings of affiliates		25.2		88.5	51.9
Other income		0.1		0.6	0.2
Revenues And Other Income		91.4		386.4	245.3
Costs and Expenses
Operating and maintenance expenses		15.5		71.0	47.8
Depreciation		5.7		37.9	16.1
General and administrative expenses		6.2		25.1	20.0
Taxes other than income taxes		2.4		10.5	6.8
Interest and debt expense		9.2		30.8	24.6
Other expenses				0.1	0.1
Total costs and expenses		39.0		175.4	115.4
Income before income taxes		52.4		211.0	129.9
Provision for income taxes		0.1		0.8	0.2
Net Income		52.3		210.2
Net Income					129.7
Less: Net income attributable to noncontrolling interests				7.3
Less: Net income (loss) attributable to Predecessors		0.0		0.0	0.0
Net income attributable to the Partnership		52.3		202.9	129.7
Acquired Assets Predecessor [Member] | Standish And Sweeny Fractionator Acquisition [Member] | Phillips 66 [Member] | Phillips 66 [Member]
Revenues and Other Income
Operating revenues—related parties		5.7		24.3	13.5
Operating revenues—third parties		0.0		0.0	0.0
Equity in earnings of affiliates		0.0		0.0	0.0
Other income		0.0		0.2	0.0
Revenues And Other Income		5.7		24.5	13.5
Costs and Expenses
Operating and maintenance expenses		4.8		5.4	8.5
Depreciation		0.4		5.6	0.7
General and administrative expenses		1.2		0.9	3.2
Taxes other than income taxes		0.7		1.8	2.1
Interest and debt expense		0.0		0.0	0.0
Other expenses				0.0	0.0
Total costs and expenses		7.1		13.7	14.5
Income before income taxes		(1.4)		10.8	(1.0)
Provision for income taxes		0.0		0.0	0.0
Net Income		(1.4)		10.8
Net Income					(1.0)
Less: Net income attributable to noncontrolling interests				(7.3)
Less: Net income (loss) attributable to Predecessors		(1.4)		18.1	(1.0)
Net income attributable to the Partnership		$ 0.0		$ 0.0	$ 0.0

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