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Earnings Per Share
 3 Months Ended
Mar. 31, 2021
Earnings Per Share [Abstract]  
Earnings Per Share Earnings Per Share
The calculations of earnings per share are as follows:
 Three Months Ended
March 31,
($ and shares in millions except per share amounts)20212020
Net income attributable to Merck & Co., Inc.
$3,179 $3,219 
Average common shares outstanding2,531 2,533 
Common shares issuable (1)
10 14 
Average common shares outstanding assuming dilution 2,541 2,547 
Basic earnings per common share attributable to Merck & Co., Inc. common shareholders
$1.26 $1.27 
Earnings per common share assuming dilution attributable to Merck & Co., Inc. common shareholders
$1.25 $1.26 
(1)Issuable primarily under share-based compensation plans.
For the first quarter of 2021 and 2020, 14 million and 2 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.