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Earnings per Share
 12 Months Ended
Dec. 31, 2017
Earnings Per Share [Abstract]  
Earnings per Share
Earnings per Share
The calculations of earnings per share (shares in millions) are as follows:
Years Ended December 31
2017
 
2016
 
2015
Net income attributable to Merck & Co., Inc.
$
2,394

 
$
3,920

 
$
4,442

Average common shares outstanding
2,730

 
2,766

 
2,816

Common shares issuable (1)
18

 
21

 
25

Average common shares outstanding assuming dilution
2,748

 
2,787

 
2,841

Basic earnings per common share attributable to Merck & Co., Inc. common shareholders
$
0.88

 
$
1.42

 
$
1.58

Earnings per common share assuming dilution attributable to Merck & Co., Inc. common shareholders
$
0.87

 
$
1.41

 
$
1.56

(1) 
Issuable primarily under share-based compensation plans.
In 2017, 2016 and 2015, 5 million, 13 million and 9 million, respectively, of common shares issuable under share-based compensation plans were excluded from the computation of earnings per common share assuming dilution because the effect would have been antidilutive.