Document and Entity Information	9 Months Ended
	Sep. 30, 2012	Oct. 31, 2012
Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q3
Trading Symbol	ub
Entity Registrant Name	UNIONBANCAL CORP
Entity Central Index Key	0001011659
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		136,330,830