EARNINGS PER COMMON SHARE

12 Months Ended

Dec. 31, 2017

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



	2017		2016		2015
Numerator (basic and diluted):
Income from continuing operations	$	533	$	491	$	357
Less: Allocation to unvested restricted stock awards	5		6		5
Income from continuing operations attributable to common shareholders	528		485		352
Loss from discontinued operations, net	—		—		(2		)
Less: Allocation to unvested restricted stock awards	—		—		—
Loss from discontinued operations attributable to common shareholders	—		—		(2		)
Net income available to common shareholders	$	528	$	485	$	350

Denominator:
Basic common shares (based upon weighted average)	314		326		338
Add: Stock option dilution	4		4		3
Diluted common shares	318		330		341

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 earnings per common share, using the "two-class method." The two-class method of computing earnings per common share is an allocation method that calculates earnings 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, 2017, 2016 and 2015, we allocated dividends and undistributed earnings to the participating securities.

R. EARNINGS PER COMMON SHARE (Concluded)

Additionally, 354,000, 338,000 and 5 million common shares for 2017, 2016 and 2015, respectively, related to stock options were excluded from the computation of diluted earnings per common share due to their antidilutive effect.

Common shares outstanding included on our balance sheet and for the calculation of earnings per common share do not include unvested stock awards (3 million common shares and 4 million common shares at December 31, 2017 and 2016, respectively); shares outstanding for legal requirements included all common shares that have voting rights (including unvested stock awards).