Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Jul. 31, 2020
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, 2020
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		132,076,912
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2