v3.8.0.1
Document and Entity Information - shares
9 Months Ended
Dec. 31, 2017
Feb. 01, 2018
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  
Document Fiscal Year Focus 2018  
Document Type 10-Q  
Document Fiscal Period Focus Q3  
Document Period End Date Dec. 31, 2017  
Amendment Flag false  
Entity Common Stock, Shares Outstanding   19,607,788