Revenue - Summary of Revenue by End-use Markets (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Jun. 30, 2026	Mar. 31, 2026	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2024
Disaggregation of Revenue [Line Items]
Net sales	$ 851.0	$ 811.5	$ 728.0	$ 733.7	$ 755.6	$ 727.0	$ 676.9	$ 717.6	$ 3,124.2	$ 2,877.1	$ 2,759.7
Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales									2,811.7	2,548.7	2,432.8
Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales									312.5	328.4	326.9
Operating
Disaggregation of Revenue [Line Items]
Net sales									3,209.8	2,969.0	2,854.8
Operating \| Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales									2,826.8	2,563.6	2,443.8
Operating \| Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales									383.0	405.4	411.0
Intersegment
Disaggregation of Revenue [Line Items]
Net sales									(85.6)	(91.9)	(95.1)
Intersegment \| Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales									(15.1)	(14.9)	(11.0)
Intersegment \| Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales									(70.5)	(77.0)	(84.1)
Aerospace and Defense
Disaggregation of Revenue [Line Items]
Net sales									2,035.2	1,768.6	1,538.8
Aerospace and Defense \| Operating \| Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales									1,924.7	1,679.6	1,449.9
Aerospace and Defense \| Operating \| Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales									123.1	104.0	111.1
Aerospace and Defense \| Intersegment
Disaggregation of Revenue [Line Items]
Net sales									(12.6)	(15.0)	(22.2)
Medical
Disaggregation of Revenue [Line Items]
Net sales									278.4	351.2	375.6
Medical \| Operating \| Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales									211.7	243.7	282.4
Medical \| Operating \| Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales									122.1	166.8	144.9
Medical \| Intersegment
Disaggregation of Revenue [Line Items]
Net sales									(55.4)	(59.3)	(51.7)
Energy
Disaggregation of Revenue [Line Items]
Net sales									230.6	200.3	185.8
Energy \| Operating \| Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales									222.0	193.2	177.2
Energy \| Operating \| Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales									8.6	7.1	8.6
Energy \| Intersegment
Disaggregation of Revenue [Line Items]
Net sales									0.0	0.0	0.0
Transportation
Disaggregation of Revenue [Line Items]
Net sales									100.4	113.3	149.1
Transportation \| Operating \| Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales									93.3	105.8	141.3
Transportation \| Operating \| Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales									7.2	7.9	8.2
Transportation \| Intersegment
Disaggregation of Revenue [Line Items]
Net sales									(0.1)	(0.4)	(0.4)
Industrial and Consumer
Disaggregation of Revenue [Line Items]
Net sales									401.8	359.5	415.3
Industrial and Consumer \| Operating \| Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales									375.1	341.3	393.0
Industrial and Consumer \| Operating \| Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales									44.2	35.3	40.3
Industrial and Consumer \| Intersegment
Disaggregation of Revenue [Line Items]
Net sales									(17.5)	(17.1)	(18.0)
Distribution
Disaggregation of Revenue [Line Items]
Net sales									77.8	84.2	95.1
Distribution \| Operating \| Specialty Alloys Operations
Disaggregation of Revenue [Line Items]
Net sales									0.0	0.0	0.0
Distribution \| Operating \| Performance Engineered Products
Disaggregation of Revenue [Line Items]
Net sales									77.8	84.3	97.9
Distribution \| Intersegment
Disaggregation of Revenue [Line Items]
Net sales									$ 0.0	$ (0.1)	$ (2.8)