Net Income Per Class A Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Basic Net Income per Class A Share
Net income attributable to PAGP	$ 4	$ 24	$ 69	$ 102
Diluted Net Income per Class A Share
Net income attributable to PAGP	4	24	69	102
Incremental net income attributable to PAGP resulting from assumed exchange of AAP units and AAP Management Units				138
Net income attributable to PAGP including incremental net income from assumed exchange of AAP units and AAP Management Units	$ 4	$ 24	$ 69	$ 240
Class A Shares
Basic Net Income per Class A Share
Basic weighted average Class A shares outstanding (shares)	154.0	101.0	142.0	99.0
Basic net income per Class A share (usd per share)	$ 0.03	$ 0.24	$ 0.49	$ 1.03
Diluted Net Income per Class A Share
Basic weighted average Class A shares outstanding (shares)	154.0	101.0	142.0	99.0
Dilutive shares resulting from assumed exchange of AAP units and AAP Management Units (shares)				137.0
Diluted weighted average Class A shares outstanding (shares)	154.0	101.0	142.0	236.0
Diluted net income per Class A share (usd per share)	$ 0.03	$ 0.24	$ 0.49	$ 1.02
Maximum
Net Income Per Class A Share
Dilutive LTIP awards (shares), less than	0.1	0.1	0.1	0.1