Document and Entity Information (USD $)	9 Months Ended
	Dec. 31, 2012
Document and Entity Information [Abstract]
Entity Registrant Name	AMERCO /NV/
Entity Central Index Key	0000004457
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Current Fiscal Year End Date	--03-31
Entity Filer Category	Accelerated Filer
Entity Well-known Seasoned Issuer	Yes
Entity Public Float	$ 510,020,982
Document Fiscal Year Focus	2013
Document Type	10-Q
Document Fiscal Period Focus	Q3
Document Period End Date	Dec. 31, 2012
Amendment Flag	false
Entity Common Stock, Shares Outstanding	19,607,788