INCOME PER COMMON SHARE

Reconciliations of the numerators and denominators used in the computations of basic and diluted earnings per common share were as follows, in millions:



	2018		2017		2016
Numerator (basic and diluted):
Net income	$	734	$	533	$	493
Less: Allocation to unvested restricted stock awards	7		5		6
Net income available to common shareholders	$	727	$	528	$	487

Denominator:
Basic common shares (based upon weighted average)	305		314		326
Add: Stock option dilution	2		4		4
Diluted common shares	307		318		330

We follow accounting guidance regarding determining whether instruments granted in share-based payment transactions are participating securities. This accounting guidance clarifies that share-based payment awards that entitle their holders to receive non-forfeitable dividends prior to vesting should be considered participating securities. We have granted restricted stock awards that contain non-forfeitable rights to dividends on unvested shares; such unvested restricted stock awards are considered participating securities. As participating securities, the unvested shares are required to be included in the calculation of our basic income per common share, using the "two-class method." The two-class method of computing income per common share is an allocation method that calculates income per share for each class of common stock and participating security according to dividends declared and participation rights in undistributed earnings. For the years ended December 31, 2018, 2017 and 2016, we allocated dividends and undistributed earnings to the participating securities.

Additionally, 710,000, 354,000 and 338,000 common shares for 2018, 2017 and 2016, respectively, related to stock options and 20,000 common shares for 2018 related to restricted stock units were excluded from the computation of diluted income per common share due to their antidilutive effect.

Common shares outstanding included on our balance sheet and for the calculation of income per common share do not include unvested stock awards (2 million common shares and 3 million common shares at December 31, 2018 and 2017, respectively); shares outstanding for legal requirements included all common shares that have voting rights (including unvested stock awards).