Net Income/(Loss) Per Class A Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Basic and Diluted Net Income/(Loss) per Class A Share
Net income (loss) attributable to PAGP	$ (69)	$ 16	$ 1	$ (565)
AAP Units
Net Income Per Class A Share
Antidilutive securities excluded from computation of earnings per share (per share)	51.0	63.0	51.0	64.0
AAP Management Units
Net Income Per Class A Share
Antidilutive securities excluded from computation of earnings per share (per share)	1.0	1.0	1.0	1.0
Class A Shares
Basic and Diluted Net Income/(Loss) per Class A Share
Basic weighted average Class A shares outstanding (in shares)	194.0	184.0	194.0	183.0
Diluted weighted average Class A shares outstanding (in shares)	194.0	184.0	194.0	183.0
BASIC NET INCOME/(LOSS) PER CLASS A SHARE (in dollars per share)	$ (0.35)	$ 0.09	$ 0	$ (3.08)
DILUTED NET INCOME/(LOSS) PER CLASS A SHARE (in dollars per share)	$ (0.35)	$ 0.09	$ 0	$ (3.08)
Maximum
Net Income Per Class A Share
Dilutive LTIP awards (shares)	0.1		0.1