STATEMENTS OF CONSOLIDATED STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions		Total	Common Stock		Additional Paid in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income
Beginning balance at Dec. 31, 2022		$ 631.2	$ 0.2		$ 1,090.4	$ 13.3	$ (475.9)	$ 3.2
Beginning balance (shares) at Dec. 31, 2022			15,940,756
Net income		15.9				15.9
Other comprehensive (loss) income, net of tax		(1.1)						(1.1)
Common shares issued (including impacts from Long-Term Incentive programs) (shares)			49,128
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued		(1.3)			(1.3)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued (shares)			(15,848)
Cash dividends declared	[1]	(12.5)				(12.5)
Amortization of unearned equity compensation		3.4			3.4
Ending balance at Mar. 31, 2023		635.6	$ 0.2		1,092.5	16.7	(475.9)	2.1
Ending balance (shares) at Mar. 31, 2023			15,974,036
Beginning balance at Dec. 31, 2023		$ 652.2	$ 0.2		1,104.7	10.1	(475.9)	13.1
Beginning balance (shares) at Dec. 31, 2023		16,015,791	16,015,791	[2]
Net income		$ 24.6				24.6
Other comprehensive (loss) income, net of tax		(2.1)						(2.1)
Common shares issued (including impacts from Long-Term Incentive programs) (shares)	[2]		56,416
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued		(1.2)			(1.2)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued (shares)	[2]		(16,175)
Cash dividends declared	[3]	(12.6)				(12.6)
Amortization of unearned equity compensation		4.0			4.0
Ending balance at Mar. 31, 2024		$ 664.9	$ 0.2		$ 1,107.5	$ 22.1	$ (475.9)	$ 11.0
Ending balance (shares) at Mar. 31, 2024		16,056,032	16,056,032	[2]

[1] Dividends declared per common share were $0.77 for the quarter ended March 31, 2023.

[2] At March 31, 2024, 345,130 shares were available for awards under the Kaiser Aluminum Corporation 2021 Equity and Incentive Compensation Plan

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