Earnings per Share/Limited Partner Unit - Partnership's Calculation of Earnings per Share Limited Partner Unit (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended									9 Months Ended
		Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019		Jun. 30, 2019	[1]	Mar. 31, 2019	[1]	Sep. 30, 2020	Sep. 30, 2019
Limited Partners Capital Account [Line Items]
Net income		$ 115.8	$ 107.8	$ 129.0	$ 87.4	[1]	$ 74.4		$ 80.8		$ 352.6	$ 242.6	[1]
Less: Net income (loss) attributable to net parent investment	[1]				(13.0)							(44.0)
Less: Net income (loss) attributable to noncontrolling interest		110.2			81.3	[1]					335.2	232.6	[1]
Net income attributable to Hess Midstream LP		5.6			19.1	[1]					17.4	54.0	[1]
Less: General partner's interest in net income	[1]				1.3							3.1
Limited partners' interest in net income		$ 5.6			17.8	[1]					$ 17.4	50.9	[1]
Common Units
Limited Partners Capital Account [Line Items]
Common unitholders' interest in net income attributable to Hess Midstream LP					$ 8.9							$ 25.5
Net income attributable to Hess Midstream LP per limited partner unit (basic and diluted):
Basic and diluted	[1]				$ 0.33							$ 0.93
Weighted average limited partner units outstanding prior to the Restructuring, Basic:
Units outstanding prior to the Restructuring, Basic	[1]				27.3							27.3
Weighted average limited partner units outstanding prior to the Restructuring, Diluted:
Units outstanding prior to the Restructuring, Diluted	[1]				27.5							27.5
Subordinated Units
Limited Partners Capital Account [Line Items]
Common unitholders' interest in net income attributable to Hess Midstream LP					$ 8.9							$ 25.4
Net income attributable to Hess Midstream LP per limited partner unit (basic and diluted):
Basic and diluted	[1]				$ 0.33							$ 0.93
Weighted average limited partner units outstanding prior to the Restructuring, Basic:
Units outstanding prior to the Restructuring, Basic	[1]				27.3							27.3
Weighted average limited partner units outstanding prior to the Restructuring, Diluted:
Units outstanding prior to the Restructuring, Diluted	[1]				27.3							27.3
Class A Shares
Net income attributable to Hess Midstream LP per Class A share:
Net income attributable to Hess Midstream LP per Class A share, Basic		$ 0.31									$ 0.97
Net income attributable to Hess Midstream LP per Class A share, Diluted		$ 0.31									$ 0.95
Net income attributable to Hess Midstream LP per limited partner unit (basic and diluted):
Weighted average Class A shares outstanding subsequent to the restructuring, Basic		18.0									18.0
Weighted average Class A shares outstanding subsequent to the restructuring, Diluted		18.1									18.1

[1] The financial information presented in this report has been retrospectively adjusted for the acquisition of Hess Infrastructure Partners LP.