Per Share Information (Tables)

12 Months Ended

Dec. 28, 2025

Earnings Per Share [Abstract]

Schedule of Basic and Diluted Income Per Common Share

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

(In millions, except per share amounts)

	Fiscal Year
	2025		2024		2023
Numerator:
Numerator for basic net income per common share -
Net income attributable to ATI	$	404.3	$	367.8	$	410.8
Effect of dilutive securities:
3.5% Convertible Senior Notes due 2025	—		5.9		10.6
Numerator for diluted net income per common share -
Net income attributable to ATI after assumed conversions	$	404.3	$	373.7	$	421.4
Denominator:
Denominator for basic net income per common share—weighted average shares	138.6		130.4		128.1
Effect of dilutive securities:
Share-based compensation	3.2		3.2		3.1
3.5% Convertible Senior Notes due 2025	—		13.0		18.8
Denominator for diluted net income per common share—adjusted weighted average shares and assumed conversions	141.8		146.6		150.0
Basic net income attributable to ATI per common share	$	2.92	$	2.82	$	3.21
Diluted net income attributable to ATI per common share	$	2.85	$	2.55	$	2.81