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, 2023	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant date fair value	$ 104.87	$ 122.22	$ 151.98
Grant date stock price	$ 84.33	$ 95.13	$ 114.71
Expected volatility of Kaiser Aluminum	49.72%	49.37%	45.71%
Expected volatility of peer companies	45.14%	51.08%	50.69%
Risk-free interest rate	4.59%	1.59%	0.29%
Dividend yield	3.65%	3.24%	2.51%