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	[1]		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)	[1]		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)	[1]		(20,625)
Cash dividends declared	[2]	(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	[1]		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	[1]		15,812,169
Net income (loss)		(17.9)
Other comprehensive income (loss), net of tax		25.0
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	[1]		15,859,820
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	[1]		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)	[1]		12,291
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)	[1]		(409)
Cash dividends declared	[2]	(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	[1]		15,859,820
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	[3],[4]
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)	[3],[4]		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)	[3],[4]		(19,643)
Cash dividends declared	[5]	(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	[3],[4]		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	[3],[4]
Net income (loss)		$ (5.7)
Other comprehensive income (loss), net of tax		(17.6)
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		15,922,062	15,922,062	[3],[4]
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	[3],[4]		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)	[3],[4]		18,101
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)	[3],[4]		(155)
Cash dividends declared	[5]	(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		15,922,062	15,922,062	[3],[4]

[1] There were no repurchases of common stock during the quarters ended March 31, 2021 and June 30, 2021.

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

[3] At June 30, 2022, 601,642 shares were available for awards under the Kaiser Aluminum Corporation 2021 Equity and Incentive Compensation Plan (“2021 Plan”).

[4] There were no repurchases of common stock during the quarters ended March 31, 2022 and June 30, 2022. At June 30, 2022, $93.1 million remained available to repurchase our common shares pursuant to the stock repurchase program.

[5] Dividends declared per common share were $0.77 for the quarters ended March 31, 2022 and June 30, 2022.