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



	Year Ended December 31,
	2018			2017			2016
Basic Net Income per Common Unit
Net income attributable to PAA	$	2,216		$	856		$	726
Distributions to Series A preferred unitholders	(149		)	(142		)	(122		)
Distributions to Series B preferred unitholders	(49		)	(11		)	—
Distributions to general partner	—			—			(412		)
Distributions to participating securities	(3		)	(2		)	(4		)
Undistributed loss allocated to general partner	—			—			14
Other	(6		)	(16		)	(2		)
Net income allocated to common unitholders ⁽¹⁾	$	2,009		$	685		$	200

Basic weighted average common units outstanding ⁽²⁾	726			717			464

Basic net income per common unit	$	2.77		$	0.96		$	0.43

Diluted Net Income per Common Unit
Net income attributable to PAA	$	2,216		$	856		$	726
Distributions to Series A preferred unitholders	—			(142		)	(122		)
Distributions to Series B preferred unitholders	(49		)	(11		)	—
Distributions to general partner	—			—			(412		)
Distributions to participating securities	(3		)	(2		)	(4		)
Undistributed loss allocated to general partner	—			—			14
Other	—			(16		)	(2		)
Net income allocated to common unitholders ⁽¹⁾	$	2,164		$	685		$	200

Basic weighted average common units outstanding ⁽²⁾	726			717			464
Effect of dilutive securities:
Series A preferred units	71			—			—
Equity-indexed compensation plan awards	2			1			2
Diluted weighted average common units outstanding	799			718			466

Diluted net income per common unit	$	2.71		$	0.95		$	0.43

⁽¹⁾

We calculate net income allocated to common unitholders based on the distributions pertaining to the current period’s net income (whether paid in cash or in-kind). After adjusting for the appropriate period’s distributions, the remaining undistributed earnings or excess distributions over earnings (“undistributed loss”), if any, are allocated to the general partner (for periods prior to the Simplification Transactions), common unitholders and participating securities in accordance with the contractual terms of our partnership agreement in effect for the period and as further prescribed under the two-class method.


⁽²⁾	We considered the common units issued in connection with the Simplification Transactions to be outstanding for the entire fourth quarter of 2016 in the calculation of weighted average common units outstanding to more closely reflect the ownership interests in us with rights to the distributions for the periods included in the calculation of net income allocated to common unitholders.