Per Share Information (Tables)

12 Months Ended

Dec. 31, 2020

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,	2020		2019		2018
Numerator:
Numerator for basic net income (loss) per common share -
Net income (loss) attributable to ATI	$	(1,572.6)	$	257.6	$	222.4
Effect of dilutive securities:
4.75% Convertible Senior Notes due 2022	—		12.8		12.9
3.5% Convertible Senior Notes due 2025	—		—		—
Numerator for diluted net income (loss) per common share -
Net income (loss) attributable to ATI after assumed conversions	$	(1,572.6)	$	270.4	$	235.3
Denominator:
Denominator for basic net income (loss) per common share—weighted average shares	126.5		125.8		125.2
Effect of dilutive securities:
Share-based compensation	—		0.8		0.8
4.75% Convertible Senior Notes due 2022	—		19.9		19.9
3.5% Convertible Senior Notes due 2025	—		—		—
Denominator for diluted net income (loss) per common share—adjusted weighted average shares and assumed conversions	126.5		146.5		145.9
Basic net income (loss) attributable to ATI per common share	$	(12.43)	$	2.05	$	1.78
Diluted net income (loss) attributable to ATI per common share	$	(12.43)	$	1.85	$	1.61