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, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant date fair value	$ 151.98	$ 105.88	$ 134.72
Grant date stock price	$ 114.71	$ 91.22	$ 108.79
Expected volatility of Kaiser Aluminum	45.71%	27.40%	27.35%
Expected volatility of peer companies	50.69%	36.94%	39.08%
Risk-free interest rate	0.29%	0.58%	2.51%
Dividend yield	2.51%	2.96%	2.21%