Debt (Tables)

9 Months Ended

Sep. 30, 2023

Debt Disclosure [Abstract]

Schedule of Debt Instruments

Debt at September 30, 2023 and December 31, 2022 was as follows (in millions): 

	September 30, 2023		December 31, 2022
ATI Inc. 7.25% Notes due 2030	$	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	11.2		19.4
Finance leases and other	103.3		79.4
Debt issuance costs	(20.7)		(17.2)
Debt	2,185.2		1,748.0
Short-term debt and current portion of long-term debt	37.5		41.7
Long-term debt	$	2,147.7	$	1,706.3

(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:

	Three months ended September 30,				Nine months ended September 30,
(in millions)	2023		2022		2023		2022
Contractual coupon rate	$	2.5	$	2.5	$	7.6	$	7.6
Amortization of debt issuance costs	0.5		0.4		1.4		1.3
Total interest expense	$	3.0	$	2.9	$	9.0	$	8.9