Document and Entity Information - shares	6 Months Ended
	Sep. 30, 2018	Nov. 02, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	AMERCO /NV/
Entity Central Index Key	0000004457
Entity Current Reporting Status	Yes
Entity Small Business	false
Current Fiscal Year End Date	--03-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Document Fiscal Year Focus	2019
Document Type	10-Q
Document Fiscal Period Focus	Q2
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Entity Common Stock, Shares Outstanding		19,607,788