Per Share Information (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Schedule earnings per share

The following table sets forth the computation of basic and diluted net income (loss) per common share:

(In millions, except per share amounts)

For the Years Ended December 31,	2019		2018		2017
Numerator:
Numerator for basic net income (loss) per common share -
Net income (loss) attributable to ATI	$	257.6	$	222.4	$	(91.9	)
Effect of dilutive securities:
4.75% Convertible Senior Notes due 2022	12.8		12.9		—
Numerator for diluted net income (loss) per common share -
Net income (loss) attributable to ATI after assumed conversions	$	270.4	$	235.3	$	(91.9	)
Denominator:
Denominator for basic net income (loss) per common share—weighted average shares	125.8		125.2		110.1
Effect of dilutive securities:
Share-based compensation	0.8		0.8		—
4.75% Convertible Senior Notes due 2022	19.9		19.9		—
Denominator for diluted net income (loss) per common share—adjusted weighted average shares and assumed conversions	146.5		145.9		110.1
Basic net income (loss) attributable to ATI per common share	$	2.05	$	1.78	$	(0.83	)
Diluted net income (loss) attributable to ATI per common share	$	1.85	$	1.61	$	(0.83	)