Employee Benefits - Benefit Obligations and Funded Status of Pension Plans, OPEB and Salaried VEBAs (Parenthetical) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($)
Kaiser Aluminum Canada Limited Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, obligation associated for salaried employees	$ 4.5