STATEMENTS OF CONSOLIDATED STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions		Total	Common Stock		Additional Paid in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive (Loss) Income
Beginning balance at Dec. 31, 2021		$ 692.5	$ 0.2		$ 1,078.9	$ 93.0	$ (475.9)	$ (3.7)
Beginning balance (shares) at Dec. 31, 2021			15,865,118
Net income		8.1				8.1
Other comprehensive (loss) income, net of tax		18.0						18.0
Common shares issued (including impacts from Long-Term Incentive programs) (shares)			58,641
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(1.9)			(1.9)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(19,643)
Cash dividends declared	[1]	(12.5)				(12.5)
Amortization of unearned equity compensation		4.0			4.0
Ending balance at Mar. 31, 2022		708.2	$ 0.2		1,081.0	88.6	(475.9)	14.3
Ending balance (shares) at Mar. 31, 2022			15,904,116
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	15,940,756	[2]
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)	[2]		49,128
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(1.3)			(1.3)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)	[2]		(15,848)
Cash dividends declared	[3]	(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	15,974,036	[2]

[1] Dividends declared per common share were $0.77 for the quarter ended March 31, 2022.

[2] At March 31, 2023, 524,804 shares were available for awards under the Kaiser Aluminum Corporation 2021 Equity and Incentive Compensation Plan (“2021 Plan”)

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