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Net Income Per Class A Share (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Basic and Diluted Net Income per Class A Share    
Net income attributable to PAGP $ 31us-gaap_NetIncomeLoss $ 14us-gaap_NetIncomeLoss
Basic and diluted weighted average Class A shares outstanding 212us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted 135us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted
Basic and diluted net income per Class A share $ 0.14us-gaap_EarningsPerShareBasicAndDiluted $ 0.11us-gaap_EarningsPerShareBasicAndDiluted
Maximum    
Basic and diluted earnings per share    
Effect of dilutive securities: Weighted average LTIP shares 0.1us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 0.1us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
/ us-gaap_RangeAxis
= us-gaap_MaximumMember