Per Share Information (Tables)

3 Months Ended

Mar. 29, 2026

Earnings Per Share [Abstract]

Schedule of Basic and Diluted Income Per Common Share

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

(In millions, except per share amounts)	Quarter ended
	March 29, 2026		March 30, 2025
Numerator:
Numerator for basic income per common share –
Net income attributable to ATI	$	118.2	$	97.0
Denominator:
Denominator for basic net income per common share – weighted average shares	136.7		141.7
Effect of dilutive securities:
Share-based compensation	1.9		2.5
Denominator for diluted net income per common share – adjusted weighted average shares and assumed conversions	138.6		144.2
Basic net income attributable to ATI per common share	$	0.86	$	0.68
Diluted net income attributable to ATI per common share	$	0.85	$	0.67