Document and Entity Information - USD ($)	12 Months Ended
	Mar. 31, 2018	May 25, 2018	Sep. 30, 2017
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	Large Accelerated Filer
Entity Well-known Seasoned Issuer	Yes
Entity Public Float			$ 2,624,776,498
Document Fiscal Year Focus	2018
Document Type	10-K
Document Fiscal Period Focus	FY
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Entity Common Stock, Shares Outstanding		19,607,788