Per Share Information (Tables)

12 Months Ended

Dec. 31, 2022

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,	2022		2021		2020
Numerator:
Numerator for basic net income (loss) per common share -
Net income (loss) attributable to ATI	$	130.9	$	(38.2)	$	(1,572.6)
Effect of dilutive securities:
4.75% Convertible Senior Notes due 2022	2.2		—		—
3.5% Convertible Senior Notes due 2025	11.3		—		—
Numerator for diluted net income (loss) per common share -
Net income (loss) attributable to ATI after assumed conversions	$	144.4	$	(38.2)	$	(1,572.6)
Denominator:
Denominator for basic net income (loss) per common share—weighted average shares	127.5		127.1		126.5
Effect of dilutive securities:
Share-based compensation	2.1		—		—
4.75% Convertible Senior Notes due 2022	2.8		—		—
3.5% Convertible Senior Notes due 2025	18.8		—		—
Denominator for diluted net income (loss) per common share—adjusted weighted average shares and assumed conversions	151.2		127.1		126.5
Basic net income (loss) attributable to ATI per common share	$	1.03	$	(0.30)	$	(12.43)
Diluted net income (loss) attributable to ATI per common share	$	0.96	$	(0.30)	$	(12.43)