Fair Value Measurements - Narrative (Details)	Mar. 31, 2026 USD ($)	Feb. 02, 2026 USD ($) MW	Dec. 31, 2025 USD ($)	Mar. 31, 2025 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset group fair value	$ 238,100,000		$ 124,300,000
Liabilities, fair value	120,600,000		66,000,000.0
Discontinued Operations, Disposed of by Sale | Hawesville Facility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Data center operations output triggering level | MW		375
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset group fair value	0		0	$ 0
Liabilities, fair value	$ 0		$ 0	$ 0
Level 3 | Scenario-based approach with the Black-Scholes option pricing model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity method investment		$ 97,000,000.0