STATEMENTS OF CONSOLIDATED STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions		Total		Common Stock		Additional Paid in Capital	Retained Earnings		Treasury Stock	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2023		$ 652.2	[1]	$ 0.2		$ 1,104.7	$ 10.1	[1]	$ (475.9)	$ 13.1
Beginning balance (Cumulative Effect of Change in Inventory Valuation Methodology, Net of Tax) at Dec. 31, 2023	[1]	56.2					56.2
Beginning balance (shares) at Dec. 31, 2023				16,015,791
Net income	[1]	18.2	[2]				18.2
Other comprehensive (loss) income, net of tax		(2.1)	[1]							(2.1)
Common shares issued (including impacts from Long-Term Incentive programs) (shares)				56,416
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued		(1.2)	[1]			(1.2)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued (shares)				(16,175)
Cash dividends declared	[1],[3]	(12.6)					(12.6)
Amortization of unearned equity compensation		4.0	[1]			4.0
Ending balance at Mar. 31, 2024	[1]	714.7		$ 0.2		1,107.5	71.9		(475.9)	11.0
Ending balance (shares) at Mar. 31, 2024	[1]			16,056,032
Beginning balance at Dec. 31, 2024	[1]	$ 743.1		$ 0.2		1,117.0	81.3		(475.9)	20.5
Beginning balance (shares) at Dec. 31, 2024		16,095,898		16,095,898	[1],[4]
Net income		$ 21.6	[2]				21.6
Other comprehensive (loss) income, net of tax		2.6								2.6
Common shares issued (including impacts from Long-Term Incentive programs) (shares)	[4]			84,115
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued		(1.8)				(1.8)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued (shares)	[4]			(25,637)
Cash dividends declared	[5]	(12.9)					(12.9)
Amortization of unearned equity compensation		4.2				4.2
Ending balance at Mar. 31, 2025		$ 756.8		$ 0.2		$ 1,119.4	$ 90.0		$ (475.9)	$ 23.1
Ending balance (shares) at Mar. 31, 2025		16,154,376		16,154,376	[4]

[1] Adjusted to reflect the retrospective change in inventory valuation methodology from LIFO to WAC. See Note 14 for further discussion.

[2] See Note 12 for supplemental cash flow information.

[3] Dividends declared per common share were $0.77 for the quarter ended March 31, 2024.

[4] At March 31, 2025, 460,763 shares were available for awards under the Kaiser Aluminum Corporation 2021 Equity and Incentive Compensation Plan, as amended and restated.

[5] Dividends declared per common share were $0.77 for the quarter ended March 31, 2025.