Debt instrument, issuance month year range, end.

No definition available.

Name:	kalu_DebtInstrumentIssuanceMonthYearRangeEnd
Namespace Prefix:	kalu_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument, issuance month year range, start.

+ References

No definition available.

+ Details

Name:	kalu_DebtInstrumentIssuanceMonthYearRangeStart
Namespace Prefix:	kalu_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument, maturity month year.

+ References

No definition available.

+ Details

Name:	kalu_DebtInstrumentMaturityMonthYear
Namespace Prefix:	kalu_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Date the debt instrument was issued, in YYYY-MM-DD format.

+ References

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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+ Details

Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

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+ Details

Name:	us-gaap_UnamortizedDebtIssuanceExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=kalu_SeniorNotesDueTwoThousandAndTwentyFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

Debt and Credit Facility - Summary of Senior Notes (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2022	Dec. 31, 2021	May 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Senior Notes
Debt Instrument [Line Items]
Total debt	$ 1,050.0	$ 1,050.0
Unamortized issuance costs	(12.8)	(13.7)
Total carrying amount	$ 1,037.2	1,036.3
4.50% Senior Notes \| Senior Notes
Debt Instrument [Line Items]
Issuance Date	May 21, 2021
Debt Instrument, Maturity Date	2031-06
Effective interest rate (percent)	4.70%
Total debt	$ 550.0	550.0
6.50% Senior Notes
Debt Instrument [Line Items]
Unamortized issuance costs			$ (5.0)
6.50% Senior Notes \| Senior Notes
Debt Instrument [Line Items]
Issuance Date, Start	2020-04
Issuance Date, End	2020-05
Debt Instrument, Maturity Date	2025-05
Effective interest rate (percent)	6.80%
Total debt				$ 350.0
4.625% Senior Notes \| Senior Notes
Debt Instrument [Line Items]
Issuance Date	Nov. 30, 2019
Debt Instrument, Maturity Date	2028-03
Effective interest rate (percent)	4.80%
Total debt	$ 500.0	$ 500.0			$ 500.0