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, 2020		$ 732.4	$ 0.2		$ 1,068.6	$ 158.2	$ (475.9)	$ (18.7)
Beginning balance (shares) at Dec. 31, 2020			15,812,169
Net income (loss)		4.5				4.5
Other comprehensive income (loss), net of tax		9.1						9.1
Common shares issued (including impacts from Long-Term Incentive programs) (shares)			56,394
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(2.4)			(2.4)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(20,625)
Cash dividends declared	[1]	(11.7)				(11.7)
Amortization of unearned equity compensation		3.1			3.1
Ending balance at Mar. 31, 2021		735.0	$ 0.2		1,069.3	151.0	(475.9)	(9.6)
Ending balance (shares) at Mar. 31, 2021			15,847,938
Beginning balance at Dec. 31, 2020		732.4	$ 0.2		1,068.6	158.2	(475.9)	(18.7)
Beginning balance (shares) at Dec. 31, 2020			15,812,169
Net income (loss)		(20.2)
Other comprehensive income (loss), net of tax		35.8
Ending balance at Sep. 30, 2021		721.0	$ 0.2		1,076.6	103.0	(475.9)	17.1
Ending balance (shares) at Sep. 30, 2021			15,862,672
Beginning balance at Mar. 31, 2021		735.0	$ 0.2		1,069.3	151.0	(475.9)	(9.6)
Beginning balance (shares) at Mar. 31, 2021			15,847,938
Net income (loss)		(22.4)				(22.4)
Other comprehensive income (loss), net of tax		15.9						15.9
Common shares issued (including impacts from Long-Term Incentive programs)		0.3			0.3
Common shares issued (including impacts from Long-Term Incentive programs) (shares)			12,291
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(409)
Cash dividends declared	[1]	(11.7)				(11.7)
Amortization of unearned equity compensation		3.6			3.6
Ending balance at Jun. 30, 2021		720.7	$ 0.2		1,073.2	116.9	(475.9)	6.3
Ending balance (shares) at Jun. 30, 2021			15,859,820
Net income (loss)		(2.3)				(2.3)
Other comprehensive income (loss), net of tax		10.8						10.8
Common shares issued (including impacts from Long-Term Incentive programs) (shares)			3,431
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(0.1)			(0.1)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(579)
Cash dividends declared	[1]	(11.6)				(11.6)
Amortization of unearned equity compensation		3.5			3.5
Ending balance at Sep. 30, 2021		721.0	$ 0.2		1,076.6	103.0	(475.9)	17.1
Ending balance (shares) at Sep. 30, 2021			15,862,672
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	15,865,118	[2]
Net income (loss)		$ 8.1				8.1
Other comprehensive income (loss), net of tax		18.0						18.0
Common shares issued (including impacts from Long-Term Incentive programs) (shares)	[2]		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)	[2]		(19,643)
Cash dividends declared	[3]	(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	[2]		15,904,116
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	15,865,118	[2]
Net income (loss)		$ (3.2)
Other comprehensive income (loss), net of tax		(18.0)
Ending balance at Sep. 30, 2022		$ 642.0	$ 0.2		1,087.2	52.2	(475.9)	(21.7)
Ending balance (shares) at Sep. 30, 2022		15,940,580	15,940,580	[2]
Beginning balance at Mar. 31, 2022		$ 708.2	$ 0.2		1,081.0	88.6	(475.9)	14.3
Beginning balance (shares) at Mar. 31, 2022	[2]		15,904,116
Net income (loss)		(13.8)				(13.8)
Other comprehensive income (loss), net of tax		(35.6)						(35.6)
Common shares issued (including impacts from Long-Term Incentive programs)		0.6			0.6
Common shares issued (including impacts from Long-Term Incentive programs) (shares)	[2]		18,101
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)	[2]		(155)
Cash dividends declared	[3]	(12.6)				(12.6)
Amortization of unearned equity compensation		3.2			3.2
Ending balance at Jun. 30, 2022		650.0	$ 0.2		1,084.8	62.2	(475.9)	(21.3)
Ending balance (shares) at Jun. 30, 2022	[2]		15,922,062
Net income (loss)		2.5				2.5
Other comprehensive income (loss), net of tax		(0.4)						(0.4)
Common shares issued (including impacts from Long-Term Incentive programs) (shares)	[2]		30,476
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(0.9)			(0.9)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)	[2]		(11,958)
Cash dividends declared	[3]	(12.5)				(12.5)
Amortization of unearned equity compensation		3.3			3.3
Ending balance at Sep. 30, 2022		$ 642.0	$ 0.2		$ 1,087.2	$ 52.2	$ (475.9)	$ (21.7)
Ending balance (shares) at Sep. 30, 2022		15,940,580	15,940,580	[2]

[1] Dividends declared per common share were $0.72 for the quarters ended March 31, 2021, June 30, 2021 and September 30, 2021.

[2] At September 30, 2022, 614,311 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 quarters ended March 31, 2022, June 30, 2022 and September 30, 2022.