Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 22, 2018
Document Information [Line Items]
Entity Registrant Name	Kaiser Aluminum Corp
Entity Central Index Key	0000811596
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		16,501,758