Borrowings (Narratives) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Mar. 31, 2021	Jun. 30, 2021
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	$ 5,335,278		$ 5,335,278		$ 4,668,907
Debt instruments, issuance and maturity dates:
Remaining Lease Term Finance Lease Weighted Average	3				3
Interest paid related to derivative contracts [Abstract]
Interest paid in cash	$ 35,300	$ 39,100	71,400	$ 78,500
Real estate loan [Member]
Debt instruments, issuance and maturity dates:
Debt instrument, maturity year	2023
Real estate loans (revolving credit) [Member] | AMERCO [Member]
Debt instruments, interest rate, effective percentage:
Unused capacity fee	0.30%
Debt instruments, face, payment, and remaining balance amount:
Line of credit facility, maximum borrowing capacity	$ 300,000		300,000
Line of credit, current borrowing capacity	200,000		200,000
Line of credit facility, remaining borrowing capacity	$ 150,000		$ 150,000
Real estate loans (revolving credit) [Member] | AMERCO [Member] | LIBOR
Debt instruments, interest rate, effective percentage:
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	0.09%		0.09%
Applicable margin interest rate	1.38%		1.38%
Sum of LIBOR and margin, maximum rate	1.47%		1.47%
Rental Truck (amortizing loans) First Loan [Member] | AMERCO [Member] | Minimum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	1.61%		1.61%
Rental Truck (amortizing loans) First Loan [Member] | AMERCO [Member] | Maximum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	4.66%		4.66%
Finance Lease [Member] | AMERCO [Member]
Debt instruments, face, payment, and remaining balance amount:
Capitalized assets, net book value	$ 753,000		$ 753,000		$ 877,000
Lease Cost [Abstract]
Sale Leaseback Transaction Lease Terms	(7) year terms
Finance Lease [Member] | AMERCO [Member] | Minimum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	1.92%		1.92%
Finance Lease [Member] | AMERCO [Member] | Maximum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	5.04%		5.04%
Capital Lease Obligations [Member] | AMERCO [Member]
Lease Cost [Abstract]
Sale Leaseback Transaction Lease Terms	(7) years
Capital Lease Obligations [Member] | AMERCO [Member] | Minimum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	1.60%		1.60%
Capital Lease Obligations [Member] | AMERCO [Member] | Maximum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	4.22%		4.22%
Private Placement | AMERCO [Member]
Debt instruments, face, payment, and remaining balance amount:
Amount held at fixed interest rates	$ 600,000		$ 600,000
New capital lease obligiations, amount	$ 150,000
Private Placement | AMERCO [Member] | Minimum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	2.43%		2.43%
Private Placement | AMERCO [Member] | Maximum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	2.78%		2.78%
Amerco Real Estate Subsidiaries and Uhaul Company of Florida [Member] | Real estate loan [Member] | LIBOR
Debt instruments, interest rate, effective percentage:
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	0.08%		0.08%
Applicable margin interest rate	1.50%		1.50%
Sum of LIBOR and margin, maximum rate	1.58%		1.58%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Senior Mortgages [Member]
Debt instruments, interest rate, effective percentage:
Debt Weighted Average Interest Rate	4.12%		4.12%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Senior Mortgages [Member] | Minimum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	2.76%		2.76%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Senior Mortgages [Member] | Maximum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	5.50%		5.50%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Working capital loans two [Member] | AMERCO [Member]
Debt instruments, face, payment, and remaining balance amount:
Line of credit facility, maximum borrowing capacity	$ 385,000		$ 385,000
Line of credit, current borrowing capacity	$ 385,000		$ 385,000
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Working capital loans two [Member] | AMERCO [Member] | LIBOR
Debt instruments, interest rate, effective percentage:
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	0.08%		0.08%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Working capital loans two [Member] | AMERCO [Member] | LIBOR | Minimum [Member]
Debt instruments, interest rate, effective percentage:
Applicable margin interest rate	1.25%		1.25%
Sum of LIBOR and margin, maximum rate	1.33%		1.33%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Working capital loans two [Member] | AMERCO [Member] | LIBOR | Maximum [Member]
Debt instruments, interest rate, effective percentage:
Applicable margin interest rate	1.50%		1.50%
Sum of LIBOR and margin, maximum rate	1.58%		1.58%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Rental Truck Revolvers [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	2.36%		2.36%
Debt instruments, face, payment, and remaining balance amount:
Line of credit, current borrowing capacity	$ 590,000		$ 590,000
Line of credit facility, remaining borrowing capacity	548,000		548,000
Amount held at fixed interest rates	100,000		100,000
Notes, loans and leases payable	$ 373,000		$ 373,000
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Rental Truck Revolvers [Member] | LIBOR | Minimum [Member]
Debt instruments, interest rate, effective percentage:
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	0.08%		0.08%
Applicable margin interest rate	1.15%		1.15%
Sum of LIBOR and margin, maximum rate	1.24%		1.24%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Rental Truck Revolvers [Member] | LIBOR | Maximum [Member]
Debt instruments, interest rate, effective percentage:
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	0.09%		0.09%
Applicable margin interest rate	1.25%		1.25%
Sum of LIBOR and margin, maximum rate	1.33%		1.33%
Various Subsidiaries of Amerco Real Estate and Uhaul Intl [Member] | Rental Truck Revolvers [Member] | SOFR
Debt instruments, interest rate, effective percentage:
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	0.05%		0.05%
Applicable margin interest rate	1.25%		1.25%
Sum of LIBOR and margin, maximum rate	1.30%		1.30%
Debt instruments, face, payment, and remaining balance amount:
Amounts held at LIBOR plus margin	$ 175,000		$ 175,000
Amerco, Us Bank, National Association, Trustee [Member] | Other Obligations [Member]
Debt instruments, face, payment, and remaining balance amount:
Notes, loans and leases payable	89,500		89,500
Subsidiary holdings of parent company debt	$ 2,400		$ 2,400
Amerco, Us Bank, National Association, Trustee [Member] | Other Obligations [Member] | Minimum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	1.75%		1.75%
Debt instruments, issuance and maturity dates:
Debt instrument, maturity year	2021
Amerco, Us Bank, National Association, Trustee [Member] | Other Obligations [Member] | Maximum [Member]
Debt instruments, interest rate, stated percentage:
Debt instrument, interest rate, stated percentage	8.00%		8.00%
Debt instruments, issuance and maturity dates:
Debt instrument, maturity year	2049
Life Insurance [Member] | Federal Home Loan Bank [Member]
Federal Home Loan Bank, Advances, Activity for the year [Abstract]
Aggregate deposit amount						$ 65,500
Available for sale equity securities, noncurrent						119,100
Available for sale equity securities pledged as collateral						$ 72,800
Life Insurance [Member] | Federal Home Loan Bank [Member] | Minimum [Member]
Federal Home Loan Bank, Advances, Activity for the year [Abstract]
Deposit interest rate						0.00%
Life Insurance [Member] | Federal Home Loan Bank [Member] | Maximum [Member]
Federal Home Loan Bank, Advances, Activity for the year [Abstract]
Deposit interest rate						1.72%