Employee Incentive Plans - Summary of Weighted Average Inputs and Assumptions Used to Calculate Fair Value at Grant Date (Details) - TSR-Based Performance Shares - $ / shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant date fair value	$ 96.34	$ 104.87	$ 122.22
Grant date stock price	$ 71.76	$ 84.33	$ 95.13
Expected volatility of Kaiser Aluminum	45.59%	49.72%	49.37%
Expected volatility of peer companies	38.67%	45.14%	51.08%
Risk-free interest rate	4.31%	4.59%	1.59%
Dividend yield	4.29%	3.65%	3.24%