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, 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, 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		39.6
Other comprehensive (loss) income, net of tax		(2.4)
Ending balance at Sep. 30, 2023		640.7	$ 0.2		1,100.4	15.2	(475.9)	0.8
Ending balance (shares) at Sep. 30, 2023			16,013,818
Beginning balance at Mar. 31, 2023		635.6	$ 0.2		1,092.5	16.7	(475.9)	2.1
Beginning balance (shares) at Mar. 31, 2023			15,974,036
Net income		18.3				18.3
Other comprehensive (loss) income, net of tax		(7.3)						(7.3)
Common shares issued (including impacts from Long-Term Incentive programs)		0.7			0.7
Common shares issued (including impacts from Long-Term Incentive programs) (shares)			45,164
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued		(0.4)			(0.4)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued (shares)			(6,036)
Cash dividends declared	[1]	(12.6)				(12.6)
Amortization of unearned equity compensation		3.8			3.8
Ending balance at Jun. 30, 2023		638.1	$ 0.2		1,096.6	22.4	(475.9)	(5.2)
Ending balance (shares) at Jun. 30, 2023			16,013,164
Net income		5.4				5.4
Other comprehensive (loss) income, net of tax		6.0						6.0
Common shares issued (including impacts from Long-Term Incentive programs) (shares)			1,000
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued		(0.1)			(0.1)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued (shares)			(346)
Cash dividends declared	[1]	(12.6)				(12.6)
Amortization of unearned equity compensation		3.9			3.9
Ending balance at Sep. 30, 2023		640.7	$ 0.2		1,100.4	15.2	(475.9)	0.8
Ending balance (shares) at Sep. 30, 2023			16,013,818
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	[2]		16,056,032
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		$ 39.7
Other comprehensive (loss) income, net of tax		3.2
Ending balance at Sep. 30, 2024		$ 667.0	$ 0.2		1,114.6	11.8	(475.9)	16.3
Ending balance (shares) at Sep. 30, 2024		16,087,755	16,087,755	[2]
Beginning balance at Mar. 31, 2024		$ 664.9	$ 0.2		1,107.5	22.1	(475.9)	11.0
Beginning balance (shares) at Mar. 31, 2024	[2]		16,056,032
Net income		3.1				3.1
Other comprehensive (loss) income, net of tax		3.2						3.2
Common shares issued (including impacts from Long-Term Incentive programs)		0.5			0.5
Common shares issued (including impacts from Long-Term Incentive programs) (shares)	[2]		38,143
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued		(0.6)			(0.6)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued (shares)	[2]		(7,063)
Cash dividends declared	[3]	(12.7)				(12.7)
Amortization of unearned equity compensation		3.6			3.6
Ending balance at Jun. 30, 2024		662.0	$ 0.2		1,111.0	12.5	(475.9)	14.2
Ending balance (shares) at Jun. 30, 2024	[2]		16,087,112
Net income		12.0				12.0
Other comprehensive (loss) income, net of tax		2.1						2.1
Common shares issued (including impacts from Long-Term Incentive programs)		0.1			0.1
Common shares issued (including impacts from Long-Term Incentive programs) (shares)	[2]		1,000
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued (shares)	[2]		(357)
Cash dividends declared	[3]	(12.7)				(12.7)
Amortization of unearned equity compensation		3.5			3.5
Ending balance at Sep. 30, 2024		$ 667.0	$ 0.2		$ 1,114.6	$ 11.8	$ (475.9)	$ 16.3
Ending balance (shares) at Sep. 30, 2024		16,087,755	16,087,755	[2]

[1] Dividends declared per common share were $0.77 for each of the quarters ended March 31, 2023, June 30, 2023, and September 30, 2023.

[2] At September 30, 2024, 597,415 shares were available for awards under the Kaiser Aluminum Corporation 2021 Equity and Incentive Compensation Plan, as amended and restated

[3] Dividends declared per common share were $0.77 for each of the quarters ended March 31, 2024, June 30, 2024, and September 30, 2024.