Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 31, 2018
Document And Entity Information
Entity Registrant Name	MUFG Americas Holdings Corporation
Entity Central Index Key	0001011659
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		147,589,713
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Trading Symbol	ub