Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Impact to net income attributable to PAGP	$ (69)		$ 16	$ 1	$ (565)
Change in Useful Life
Property, Plant and Equipment [Line Items]
Increase in depreciation expense	18			36
Impact to net income attributable to PAGP	$ (4)			$ (7)
Class A Shares
Property, Plant and Equipment [Line Items]
Impact to basic net income per Class A share (in dollars per share)	$ (0.35)		$ 0.09	$ 0	$ (3.08)
Impact to diluted net income per Class A share (in dollars per share)	(0.35)		$ 0.09	0	$ (3.08)
Class A Shares | Change in Useful Life
Property, Plant and Equipment [Line Items]
Impact to basic net income per Class A share (in dollars per share)	(0.01)			(0.04)
Impact to diluted net income per Class A share (in dollars per share)	$ (0.01)			$ (0.04)
Pipeline and related facilities and Storage, terminal and rail facilities | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life						10 years
Pipeline and related facilities and Storage, terminal and rail facilities | Minimum | Change in Useful Life
Property, Plant and Equipment [Line Items]
Property and equipment, useful life		10 years
Pipeline and related facilities and Storage, terminal and rail facilities | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life						70 years
Pipeline and related facilities and Storage, terminal and rail facilities | Maximum | Change in Useful Life
Property, Plant and Equipment [Line Items]
Property and equipment, useful life		50 years