Sweeny Fractionator Acquisition (Schedule of Results of Operations Giving Effect to Acquisitions) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015		Dec. 31, 2015		Dec. 31, 2014
Revenues
Operating revenues—related parties	$ 94.2	$ 62.8	[1]
Operating revenues—third parties	2.0	1.1	[1]
Equity in earnings of affiliates	24.8	6.1	[1]
Other income	0.2	0.1	[1]
Total revenues and other income	121.2	70.1	[1]
Costs and Expenses
Operating and maintenance expenses	22.8	16.0	[1]
Depreciation	13.8	5.1	[1]
General and administrative expenses	8.9	8.2	[1]
Taxes other than income taxes	5.4	1.9	[1]
Interest and debt expense	9.9	5.9	[1]
Total costs and expenses	60.8	37.1	[1]
Income before income taxes	60.4	33.0	[1]
Provision for income taxes	0.2	0.2	[1]
Net Income	60.2	32.8	[1]
Less: Net income attributable to noncontrolling interests	3.0
Net income attributable to Predecessors	4.9	(2.6)	[1]
Net income attributable to the Partnership	52.3	35.4	[1]
Assets, Current [Abstract]
Cash and cash equivalents	20.1	148.6	[1]	$ 50.3	[2]	$ 15.9	[1]
Accounts receivable—related parties	36.4			21.4	[2]
Accounts receivable—third parties	1.6			3.3	[2]
Materials and supplies	5.2			4.5	[2]
Other current assets	1.6			4.2	[2]
Total Current Assets	64.9			83.7	[2]
Equity investments	967.1			944.9	[2]
Net properties, plants and equipment	1,641.5			1,625.2	[2]
Goodwill	2.5			2.5	[2]
Deferred rentals—related parties	5.4			5.6	[2]
Deferred tax assets	0.0			0.1	[2]
Other assets	0.7			0.7	[2]
Total Assets	2,682.1			2,662.7	[2]
Liabilities, Current [Abstract]
Accounts payable—related parties	5.6			3.9	[2]
Accounts payable—third parties	15.6			66.9	[2]
Payroll and benefits payable	0.0			0.7	[2]
Accrued property and other taxes	9.5			7.5	[2]
Accrued interest	5.7			16.9	[2]
Current portion of accrued environmental costs	0.8			0.8	[2]
Deferred revenues—related parties	5.8			4.6	[2]
Other current liabilities	0.2			0.1	[2]
Total Current Liabilities	43.2			101.4	[2]
Note payable—related party	212.0			241.0	[2]
Long-term debt	1,090.9			1,090.7	[2]
Asset retirement obligations	3.4			3.4	[2]
Accrued environmental costs	0.8			0.8	[2]
Deferred income taxes	0.6			0.3	[2]
Deferred revenues—related party—long-term	17.1			10.9	[1]
Total Liabilities	1,368.0			1,448.5	[2]
Equity [Abstract]
General partner—Phillips 66	(646.8)			(650.3)	[2]
Accumulated other comprehensive loss	(0.8)			(1.5)	[2]
Total Equity	1,314.1	754.8	[1]	1,214.2	[2]	412.8
Total Liabilities and Equity	2,682.1			2,662.7	[2]
Phillips 66 [Member]
Equity [Abstract]
Net investment-Predecessors	0.0			824.1	[2]
Public [Member] | Common Units [Member]
Costs and Expenses
Net income attributable to the Partnership	10.7	8.6
Equity [Abstract]
Unitholders	808.5			808.9	[2]
Total Equity	808.5	801.4	[1]	808.9		415.3
Non-public [Member] | Common Units [Member] | Phillips 66 [Member]
Costs and Expenses
Net income attributable to the Partnership	25.8	8.0
Equity [Abstract]
Unitholders	301.5			233.0	[2]
Total Equity	301.5	58.0	[1]	233.0		$ 57.1
Phillips 66 Partners LP (As Previously Reported) [Member]
Revenues
Operating revenues—related parties	76.5	62.8
Operating revenues—third parties	2.0	1.1
Equity in earnings of affiliates	24.8	6.1
Other income		0.1
Total revenues and other income	103.3	70.1
Costs and Expenses
Operating and maintenance expenses	17.6	14.8
Depreciation	8.4	5.1
General and administrative expenses	8.1	7.4
Taxes other than income taxes	3.8	1.3
Interest and debt expense	9.9	5.9
Total costs and expenses	47.8	34.5
Income before income taxes	55.5	35.6
Provision for income taxes	0.2	0.2
Net Income	55.3	35.4
Less: Net income attributable to noncontrolling interests	3.0
Net income attributable to the Partnership	52.3	35.4
Assets, Current [Abstract]
Cash and cash equivalents				48.0
Accounts receivable—related parties				21.4
Accounts receivable—third parties				3.3
Materials and supplies				2.5
Other current assets				2.2
Total Current Assets				77.4
Equity investments				944.9
Net properties, plants and equipment				492.4
Goodwill				2.5
Deferred rentals—related parties				5.6
Other assets				0.7
Total Assets				1,523.5
Liabilities, Current [Abstract]
Accounts payable—related parties				3.9
Accounts payable—third parties				8.3
Accrued property and other taxes				5.1
Accrued interest				15.1
Current portion of accrued environmental costs				0.8
Deferred revenues—related parties				4.4
Other current liabilities				0.1
Total Current Liabilities				37.7
Long-term debt				1,090.7
Asset retirement obligations				3.4
Accrued environmental costs				0.8
Deferred income taxes				0.3
Deferred revenues—related party—long-term				0.5
Total Liabilities				1,133.4
Equity [Abstract]
General partner—Phillips 66				(650.3)
Accumulated other comprehensive loss				(1.5)
Total Equity				390.1
Total Liabilities and Equity				1,523.5
Phillips 66 Partners LP (As Previously Reported) [Member] | Public [Member] | Common Units [Member]
Equity [Abstract]
Unitholders				808.9
Phillips 66 Partners LP (As Previously Reported) [Member] | Non-public [Member] | Common Units [Member] | Phillips 66 [Member]
Equity [Abstract]
Unitholders				233.0
Acquired Assets Predecessor [Member] | Sweeny Fractionator Acquisition [Member] | Phillips 66 [Member] | Phillips 66 [Member]
Revenues
Operating revenues—related parties	17.7
Other income	0.2
Total revenues and other income	17.9
Costs and Expenses
Operating and maintenance expenses	5.2	1.2
Depreciation	5.4
General and administrative expenses	0.8	0.8
Taxes other than income taxes	1.6	0.6
Total costs and expenses	13.0	2.6
Income before income taxes	4.9	(2.6)
Net Income	4.9	(2.6)
Net income attributable to Predecessors	$ 4.9	$ (2.6)
Assets, Current [Abstract]
Cash and cash equivalents				2.3
Materials and supplies				2.0
Other current assets				2.0
Total Current Assets				6.3
Net properties, plants and equipment				1,132.8
Deferred tax assets				0.1
Total Assets				1,139.2
Liabilities, Current [Abstract]
Accounts payable—third parties				58.6
Payroll and benefits payable				0.7
Accrued property and other taxes				2.4
Accrued interest				1.8
Deferred revenues—related parties				0.2
Total Current Liabilities				63.7
Note payable—related party				241.0
Deferred revenues—related party—long-term				10.4
Total Liabilities				315.1
Equity [Abstract]
Net investment-Predecessors				824.1
Total Equity				824.1
Total Liabilities and Equity				$ 1,139.2

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

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