Net Income Per Class A Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basic and Diluted Net Income per Class A Share
Net income attributable to PAGP	$ 32	$ 16	$ 93	$ 45
Basic and diluted weighted average Class A shares outstanding	225.0	136.0	220.0	136.0
Basic and diluted net income per Class A share	$ 0.14	$ 0.12	$ 0.42	$ 0.33
Maximum
Basic and diluted earnings per share
Dilutive PAGP LTIP awards (in shares)	0.1	0.1	0.1	0.1