Acquisitions - Statement of Income (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015		Sep. 30, 2016	Sep. 30, 2015
Revenue
Third parties	$ 46.1	$ 65.0	[1]	$ 149.8	$ 165.1	[1]
Related parties	21.8	31.2	[1]	65.9	76.8	[1]
Total revenue	67.9	96.2	[1]	215.7	241.9	[1]
Costs and expenses
Operations and maintenance – third parties	11.4	12.2	[1]	33.1	32.0	[1]
Operations and maintenance – related parties	5.3	4.5	[1]	15.9	14.2	[1]
General and administrative – third parties	2.2	1.8	[1]	6.2	6.8	[1]
General and administrative – related parties	5.7	6.3	[1]	17.3	17.8	[1]
Depreciation, amortization and accretion	6.0	5.4	[1]	17.7	16.0	[2]
Property and other taxes	1.3	0.9	[1]	6.4	7.6	[1]
Total costs and expenses	31.9	31.1	[1]	96.6	94.4	[1]
Operating income	36.0	65.1	[1]	119.1	147.5	[1]
Income from equity investments	21.4	24.1	[1]	70.2	47.4	[1]
Dividend income from investment	4.2	2.7	[1]	11.6	6.6	[1]
Other income	0.0	0.1	[1]	0.0	1.1	[1]
Investment, dividend and other income	25.6	26.9	[1]	81.8	55.1	[1]
Interest expense, net	2.8	1.7	[1]	7.8	2.2	[1]
Income before income taxes	58.8	90.3	[1]	193.1	200.4	[1]
Income tax expense	0.0	(0.3)	[1]	0.0	0.0	[1]
Net income	58.8	90.6	[1]	193.1	200.4	[1],[2]
Less: Net income attributable to Parent	0.0	16.2	[1]	0.0	39.3	[1]
Less: Net income attributable to noncontrolling interests	2.5	20.1	[1]	17.7	51.0	[1]
Net income attributable to the Partnership	$ 56.3	54.3	[1]	$ 175.4	110.1	[1]
Pecten
Revenue
Third parties		65.0			165.1
Related parties		31.2			76.8
Total revenue		96.2			241.9
Costs and expenses
Operations and maintenance – third parties		12.2			32.0
Operations and maintenance – related parties		4.5			14.2
General and administrative – third parties		1.8			6.8
General and administrative – related parties		6.3			17.8
Depreciation, amortization and accretion		5.4			16.0
Property and other taxes		0.9			7.6
Total costs and expenses		31.1			94.4
Operating income		65.1			147.5
Income from equity investments		24.1			47.4
Dividend income from investment		2.7			6.6
Other income		0.1			1.1
Investment, dividend and other income		26.9			55.1
Interest expense, net		1.7			2.2
Income before income taxes		90.3			200.4
Income tax expense		(0.3)			0.0
Net income		90.6			200.4
Less: Net income attributable to Parent		16.2			39.3
Less: Net income attributable to noncontrolling interests		20.1			51.0
Net income attributable to the Partnership		54.3			110.1
Shell Midstream Partners, L.P. | Pecten
Revenue
Third parties		57.5			145.3
Related parties		14.9			36.4
Total revenue		72.4			181.7
Costs and expenses
Operations and maintenance – third parties		9.2			23.8
Operations and maintenance – related parties		3.6			10.9
General and administrative – third parties		1.6			6.6
General and administrative – related parties		4.9			14.7
Depreciation, amortization and accretion		3.5			10.4
Property and other taxes		0.7			7.1
Total costs and expenses		23.5			73.5
Operating income		48.9			108.2
Income from equity investments		24.1			47.4
Dividend income from investment		2.7			6.6
Other income		0.1			1.1
Investment, dividend and other income		26.9			55.1
Interest expense, net		1.7			2.2
Income before income taxes		74.1			161.1
Income tax expense		(0.3)			0.0
Net income		74.4			161.1
Less: Net income attributable to Parent		0.0			0.0
Less: Net income attributable to noncontrolling interests		20.1			51.0
Net income attributable to the Partnership		54.3			110.1
Shell Auger and Lockport Operations | Pecten
Revenue
Third parties		7.5			19.8
Related parties		16.3			40.4
Total revenue		23.8			60.2
Costs and expenses
Operations and maintenance – third parties		3.0			8.2
Operations and maintenance – related parties		0.9			3.3
General and administrative – third parties		0.2			0.2
General and administrative – related parties		1.4			3.1
Depreciation, amortization and accretion		1.9			5.6
Property and other taxes		0.2			0.5
Total costs and expenses		7.6			20.9
Operating income		16.2			39.3
Income from equity investments		0.0			0.0
Dividend income from investment		0.0			0.0
Other income		0.0			0.0
Investment, dividend and other income		0.0			0.0
Interest expense, net		0.0			0.0
Income before income taxes		16.2			39.3
Income tax expense		0.0			0.0
Net income		16.2			39.3
Less: Net income attributable to Parent		16.2			39.3
Less: Net income attributable to noncontrolling interests		0.0			0.0
Net income attributable to the Partnership		$ 0.0			$ 0.0

[1] (1) The 2015 financial information has been retrospectively adjusted for the acquisition of the Shell Auger and Lockport Operations.

[2] (1) The 2015 financial information has been retrospectively adjusted for the acquisition of the Shell Auger and Lockport Operations.