Business, Product and Geographical Area Information - Schedule of Net Sales by End Market Segment Applications (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Net sales:
Net sales	$ 1,214.5	$ 843.5	$ 3,577.9	$ 2,444.0
Aero/HS Products
Net sales:
Net sales	291.9	182.2	884.0	624.8
Packaging
Net sales:
Net sales	561.4	393.9	1,640.2	1,049.0
GE Products
Net sales:
Net sales	278.3	192.2	799.3	559.2
Automotive Extrusions
Net sales:
Net sales	82.9	75.2	254.4	211.0
Products Transferred at a Point in Time
Net sales:
Net sales	963.8	670.7	2,809.0	1,888.1
Products Transferred Over Time
Net sales:
Net sales	$ 250.7	$ 172.8	$ 768.9	$ 555.9

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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+ Details