Net Income Per Class A Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Basic Net Income per Class A Share
Net income attributable to PAGP	$ 41	$ 36
Diluted Net Income per Class A Share
Net income attributable to PAGP	41	36
Incremental net income attributable to PAGP resulting from assumed exchange of AAP units and AAP Management Units		54
Net income attributable to PAGP including incremental net income from assumed exchange of AAP units and AAP Management Units	$ 41	$ 90
Class A Shares
Basic Net Income per Class A Share
Basic weighted average Class A shares outstanding (shares)	120.0	95.0
Basic net income per Class A share (usd per share)	$ 0.34	$ 0.39
Diluted Net Income per Class A Share
Basic weighted average Class A shares outstanding (shares)	120.0	95.0
Dilutive shares resulting from assumed exchange of AAP units and AAP Management Units (shares)		150.0
Diluted weighted average Class A shares outstanding (shares)	120.0	245.0
Diluted net income per Class A share (usd per share)	$ 0.34	$ 0.37
Maximum
Net Income Per Class A Share
Dilutive LTIP awards (shares)	0.1	0.1