Document and Entity Information - USD ($)	12 Months Ended
	Mar. 31, 2021	May 21, 2021	Sep. 30, 2020
Document and Entity Information [Abstract]
Entity Registrant Name	AMERCO
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			$ 3,206,757,547
Document Fiscal Year Focus	2021
Document Type	10-K
Document Fiscal Period Focus	FY
Document Period End Date	Mar. 31, 2021
Amendment Flag	false
Entity Common Stock, Shares Outstanding		19,607,788
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity File Number	001-11255
Entity Tax Identification Number	88-0106815
Entity Address Address Line 1	5555 Kietzke Lane
Entity Address Address Line 2	Ste. 100
Entity Address City Or Town	Reno
Entity Address State Or Province	NV
Entity Address Postal Zip Code	89511
City Area Code	775
Local Phone Number	688-6300
Security 12b Title	Common stock, $0.25 par value
Trading Symbol	UHAL
Security Exchange Name	NASDAQ
Entity Interactive Data Current	Yes
Entity Incorporation State Country Code	NV
Document Annual Report	true
Document Transition Report	false