The following table sets forth the computation of basic and diluted net income per common unit (in millions, except per unit data):

	Three Months Ended June 30,						Six Months Ended June 30,
	2016			2015			2016			2015
Basic Net Income per Common Unit
Net income attributable to PAA	$	101		$	124		$	302		$	407
Distributions to Series A preferred units (1)	(33		)	—			(55		)	—
Distributions to general partner (1)	(155		)	(152		)	(310		)	(300		)
Distributions to participating securities (1)	(1		)	(1		)	(2		)	(3		)
Undistributed loss allocated to general partner (1)	7			6			12			9

Net income/(loss) allocated to common unitholders in accordance with application of the two-class method for MLPs	$	(81	)	$	(23	)	$	(53	)	$	113


Basic weighted average common units outstanding	398			397			398			390

Basic net income/(loss) per common unit	$	(0.20	)	$	(0.06	)	$	(0.13	)	$	0.29


Diluted Net Income per Common Unit
Net income attributable to PAA	$	101		$	124		$	302		$	407
Distributions to Series A preferred units (1)	(33		)	—			(55		)	—
Distributions to general partner (1)	(155		)	(152		)	(310		)	(300		)
Distributions to participating securities (1)	(1		)	(1		)	(2		)	(3		)
Undistributed loss allocated to general partner (1)	7			6			12			9

Net income/(loss) allocated to common unitholders in accordance with application of the two-class method for MLPs	$	(81	)	$	(23	)	$	(53	)	$	113


Basic weighted average common units outstanding	398			397			398			390
Effect of dilutive securities: Weighted average LTIP units	—			—			—			3

Diluted weighted average common units outstanding	398			397			398			393


Diluted net income/(loss) per common unit	$	(0.20	)	$	(0.06	)	$	(0.13	)	$	0.29

(1)

We calculate net income allocated to common unitholders based on the distributions pertaining to the current period’s net income. After adjusting for the appropriate period’s distributions, the remaining undistributed earnings or excess distributions over earnings, if any, are allocated to the general partner, common unitholders and participating securities in accordance with the contractual terms of our partnership agreement and as further prescribed under the two-class method.