Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	Apr. 30, 2017
Document And Entity Information
Entity Registrant Name	MUFG Americas Holdings Corporation
Entity Central Index Key	0001011659
Document Type	10-Q
Document Period End Date	Mar. 31, 2017
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		144,322,280
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q1
Trading Symbol	ub