Debt (Tables)

3 Months Ended

Mar. 31, 2024

Debt Disclosure [Abstract]

Schedule of Debt Instruments

Debt at March 31, 2024 and December 31, 2023 was as follows (in millions): 

	March 31, 2024		December 31, 2023
ATI Inc. 7.25% Notes due 2030	$	425.0	$	425.0
ATI Inc. 5.875% Notes due 2027	350.0		350.0
ATI Inc. 5.125% Notes due 2031	350.0		350.0
ATI Inc. 4.875% Notes due 2029	325.0		325.0
ATI Inc. 3.5% Convertible Senior Notes due 2025	291.4		291.4
Allegheny Ludlum 6.95% Debentures due 2025 (a)	150.0		150.0
ABL Term Loan	200.0		200.0
U.S. revolving credit facility	—		—
Foreign credit facilities	—		5.0
Finance leases and other	100.6		102.8
Debt issuance costs	(18.5)		(19.6)
Debt	2,173.5		2,179.6
Short-term debt and current portion of long-term debt	27.1		31.9
Long-term debt	$	2,146.4	$	2,147.7

(a) The payment obligations of these debentures issued by Allegheny Ludlum, LLC are fully and unconditionally guaranteed by ATI.

Interest Income and Interest Expense Disclosure

Interest expense on the 2025 Convertible Notes was as follows:

	Quarter ended
(in millions)	March 31, 2024		April 2, 2023
Contractual coupon rate	$	2.5	$	2.5
Amortization of debt issuance costs	0.5		0.5
Total interest expense	$	3.0	$	3.0