Segments - Total Assets for Reportable Segments (Parenthetical) (Detail) - USD ($) $ in Millions		9 Months Ended		12 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Cash contributed to acquire equity investments	[1]		$ 33.0
Processing and Storage
Segment Reporting Information [Line Items]
Cash contributed to acquire equity investments		$ 108.2		$ 107.8

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