Net Income/(Loss) Per Class A Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic Net Income/(Loss) per Class A Share
Net income/(loss) attributable to PAGP	$ 17	$ 70	$ (548)	$ 283
Diluted Net Income/(Loss) per Class A Share
Net income/(loss) attributable to PAGP	17	70	(548)	283
Incremental net income attributable to PAGP resulting from assumed exchange of AAP Management Units	0	0	0	1
Net income/(loss) attributable to PAGP including incremental net income from assumed exchange of AAP Management Units	$ 17	$ 70	$ (548)	$ 284
AAP Units
Net Income Per Class A Share
Antidilutive securities excluded from computation of earnings per share (per share)	60.0	96.0	63.0	109.0
AAP Management Units
Net Income Per Class A Share
Antidilutive securities excluded from computation of earnings per share (per share)	1.0	2.0	1.0
Class A Shares
Basic Net Income/(Loss) per Class A Share
Basic weighted average Class A shares outstanding	186.0	168.0	184.0	163.0
Basic net income/(loss) per Class A share	$ 0.09	$ 0.41	$ (2.97)	$ 1.73
Diluted Net Income/(Loss) per Class A Share
Dilutive shares resulting from assumed exchange of AAP Management Units (in shares)	0.0	0.0	0.0	2.0
Diluted weighted average Class A shares outstanding	186.0	168.0	184.0	165.0
Diluted net income/(loss) per Class A share	$ 0.09	$ 0.41	$ (2.97)	$ 1.72
Maximum
Net Income Per Class A Share
Dilutive LTIP awards (shares)		0.1		0.1