Earnings Per Share of Common Stock (Tables)

6 Months Ended

Jun. 30, 2021

Earnings Per Share [Abstract]

Reconciliation of Earnings and Share Data used in Basic and Diluted (Losses) Earnings per Share Computations

The following table presents a reconciliation of the earnings and share data used in the basic and diluted earnings per share computations for the three and six months ended June 30, 2021 and 2020:

	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
	($ in millions, except share amounts)
Net earnings (losses) available to Alleghany stockholders	$	403.7	$	177.4	$	633.7	$	(183.8	)
Effect of dilutive securities		—		—		—		(8.4	)
Income available to common stockholders for diluted earnings per share	$	403.7	$	177.4	$	633.7	$	(192.2	)
Weighted average common shares outstanding applicable to basic earnings per share		13,919,489		14,310,874		13,954,449		14,325,772
Effect of dilutive securities		—		—		—		35,797
Adjusted weighted average common shares outstanding applicable to diluted earnings per share		13,919,489		14,310,874		13,954,449		14,361,569
Contingently issuable shares(1)						59,972		16,758

(1) Contingently issuable shares were potentially available in the periods presented, but were not included in the diluted earnings per share computations because the impact was anti-dilutive to the earnings per share calculation.