Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Mar. 31, 2022	Sep. 30, 2021
ASSETS:
Cash and cash equivalents	$ 3,065,115	$ 2,704,137
Reinsurance recoverables and trade receivables, net	203,202	229,343
Inventories, net	166,136	158,888
Prepaid expenses	236,035	236,915
Investments, fixed maturities and marketable equities	2,615,758	2,893,399
Investments, other	548,198	543,755
Deferred policy acquisition costs, net	146,778	103,828
Other assets	47,900	60,409
Right of use Assets - Financing	529,000	620,824
Right of use Assets - Operating	68,208	74,382
Related party assets	48,337	47,851
Subtotal assets	7,674,667	7,673,731
Investments in subsidiaries	0	0
Property, plant and equipment, at cost:
Land	1,427,781	1,283,142
Buildings and improvements	6,390,317	5,974,639
Furniture and equipment	876,515	846,132
Property, plant and equipment (gross)	14,509,801	13,358,406
Less: Accumulated depreciation	(4,041,125)	(3,732,556)
Total property, plant and equipment	10,468,676	9,625,850
Total assets	18,143,343	17,299,581	$ 16,337,228
Liabilities:
Accounts payable and accrued expenses	706,402	677,785
Notes, loans and leases payable	6,298,831	6,022,497
Operating lease liability	67,858	74,197
Policy benefits and losses, claims and loss expenses payable	990,233	978,254
Liabilities from investment contracts	2,390,028	2,336,238
Other policyholders' funds and liabilities	12,126	10,812
Deferred income	56,871	49,157
Deferred income taxes, net	1,307,807	1,265,358
Related party liabilities	0	0
Total liabilities	11,830,156	11,414,298
Stockholders' equity:
Additional paid-in capital	453,819	453,819
Accumulated other comprehensive loss	(192,121)	46,384
Retained earnings	6,718,642	6,052,233
Total stockholders' equity	6,313,187	5,885,283
Total liabilities and stockholders' equity	18,143,343	17,299,581
Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	727,953	615,679
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	5,087,235	4,638,814
Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Serial Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0	0
Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	10,497	10,497
Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	(525,653)	(525,653)
Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	(151,997)	(151,997)
Operating Segments [Member] | Moving and Storage Consolidations [Member]
ASSETS:
Cash and cash equivalents	3,025,390	2,643,213
Reinsurance recoverables and trade receivables, net	117,336	142,895
Inventories, net	166,136	158,888
Prepaid expenses	236,035	236,915
Investments, fixed maturities and marketable equities	0	0
Investments, other	20,653	20,653
Deferred policy acquisition costs, net	0	0
Other assets	44,194	57,305
Right of use Assets - Financing	529,000	620,824
Right of use Assets - Operating	67,107	74,190
Related party assets	66,682	64,611
Subtotal assets	4,272,533	4,019,494
Investments in subsidiaries	502,299	737,073
Property, plant and equipment, at cost:
Land	1,427,781	1,283,142
Buildings and improvements	6,390,317	5,974,639
Furniture and equipment	876,515	846,132
Property, plant and equipment (gross)	14,509,801	13,358,406
Less: Accumulated depreciation	(4,041,125)	(3,732,556)
Total property, plant and equipment	10,468,676	9,625,850
Total assets	15,243,508	14,382,417
Liabilities:
Accounts payable and accrued expenses	695,610	663,482
Notes, loans and leases payable	6,298,831	6,022,497
Operating lease liability	66,743	73,998
Policy benefits and losses, claims and loss expenses payable	436,854	418,890
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	0	0
Deferred income	56,871	49,157
Deferred income taxes, net	1,354,154	1,244,639
Related party liabilities	26,124	25,668
Total liabilities	8,935,187	8,498,331
Stockholders' equity:
Additional paid-in capital	454,029	454,029
Accumulated other comprehensive loss	(196,987)	45,187
Retained earnings	6,718,432	6,052,023
Total stockholders' equity	6,308,321	5,884,086
Total liabilities and stockholders' equity	15,243,508	14,382,417
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	727,953	615,679
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	5,087,235	4,638,814
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Serial Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0	0
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	10,497	10,497
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	(525,653)	(525,653)
Operating Segments [Member] | Moving and Storage Consolidations [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	(151,997)	(151,997)
Operating Segments [Member] | Property and Casualty Insurance [Member]
ASSETS:
Cash and cash equivalents	11,196	10,800
Reinsurance recoverables and trade receivables, net	51,720	50,235
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	267,482	297,488
Investments, other	119,926	114,269
Deferred policy acquisition costs, net	0	0
Other assets	698	371
Right of use Assets - Financing	0	0
Right of use Assets - Operating	1,039	93
Related party assets	5,862	6,713
Subtotal assets	457,923	479,969
Investments in subsidiaries	0	0
Property, plant and equipment, at cost:
Land	0	0
Buildings and improvements	0	0
Furniture and equipment	0	0
Property, plant and equipment (gross)	0	0
Less: Accumulated depreciation	0	0
Total property, plant and equipment	0	0
Total assets	457,923	479,969
Liabilities:
Accounts payable and accrued expenses	5,245	3,849
Notes, loans and leases payable	0	0
Operating lease liability	1,048	93
Policy benefits and losses, claims and loss expenses payable	156,998	160,379
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	3,633	3,521
Deferred income	0	0
Deferred income taxes, net	5,189	12,803
Related party liabilities	3,001	3,196
Total liabilities	175,114	183,841
Stockholders' equity:
Additional paid-in capital	91,120	91,120
Accumulated other comprehensive loss	(7,804)	16,630
Retained earnings	196,192	185,077
Total stockholders' equity	282,809	296,128
Total liabilities and stockholders' equity	457,923	479,969
Operating Segments [Member] | Property and Casualty Insurance [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0	0
Operating Segments [Member] | Property and Casualty Insurance [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0	0
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Operating Segments [Member] | Property and Casualty Insurance [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Operating Segments [Member] | Property and Casualty Insurance [Member] | Serial Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0	0
Operating Segments [Member] | Property and Casualty Insurance [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	3,301	3,301
Operating Segments [Member] | Property and Casualty Insurance [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	0
Operating Segments [Member] | Property and Casualty Insurance [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	0
Operating Segments [Member] | Life Insurance [Member]
ASSETS:
Cash and cash equivalents	28,529	50,124
Reinsurance recoverables and trade receivables, net	34,146	36,213
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	2,348,276	2,595,911
Investments, other	407,619	408,833
Deferred policy acquisition costs, net	146,778	103,828
Other assets	3,008	2,733
Right of use Assets - Financing	0	0
Right of use Assets - Operating	62	99
Related party assets	13,234	16,911
Subtotal assets	2,981,652	3,214,652
Investments in subsidiaries	0	0
Property, plant and equipment, at cost:
Land	0	0
Buildings and improvements	0	0
Furniture and equipment	0	0
Property, plant and equipment (gross)	0	0
Less: Accumulated depreciation	0	0
Total property, plant and equipment	0	0
Total assets	2,981,652	3,214,652
Liabilities:
Accounts payable and accrued expenses	5,547	10,454
Notes, loans and leases payable	0	0
Operating lease liability	67	106
Policy benefits and losses, claims and loss expenses payable	396,381	398,985
Liabilities from investment contracts	2,390,028	2,336,238
Other policyholders' funds and liabilities	8,493	7,291
Deferred income	0	0
Deferred income taxes, net	(51,536)	7,916
Related party liabilities	13,182	12,717
Total liabilities	2,762,162	2,773,707
Stockholders' equity:
Additional paid-in capital	26,271	26,271
Accumulated other comprehensive loss	(136,861)	87,200
Retained earnings	327,580	324,974
Total stockholders' equity	219,490	440,945
Total liabilities and stockholders' equity	2,981,652	3,214,652
Operating Segments [Member] | Life Insurance [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0	0
Operating Segments [Member] | Life Insurance [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0	0
Operating Segments [Member] | Life Insurance [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Operating Segments [Member] | Life Insurance [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Operating Segments [Member] | Life Insurance [Member] | Serial Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0	0
Operating Segments [Member] | Life Insurance [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	2,500	2,500
Operating Segments [Member] | Life Insurance [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	0
Operating Segments [Member] | Life Insurance [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	0
Consolidation, Eliminations [Member]
ASSETS:
Cash and cash equivalents	0	0
Reinsurance recoverables and trade receivables, net	0	0
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	0	0
Investments, other	0	0
Deferred policy acquisition costs, net	0	0
Other assets	0	0
Right of use Assets - Financing	0	0
Right of use Assets - Operating	0	0
Related party assets	(37,441)	(40,384)
Subtotal assets	(37,441)	(40,384)
Investments in subsidiaries	(502,299)	(737,073)
Property, plant and equipment, at cost:
Land	0	0
Buildings and improvements	0	0
Furniture and equipment	0	0
Property, plant and equipment (gross)	0	0
Less: Accumulated depreciation	0	0
Total property, plant and equipment	0	0
Total assets	(539,740)	(777,457)
Liabilities:
Accounts payable and accrued expenses	0	0
Notes, loans and leases payable	0	0
Operating lease liability	0	0
Policy benefits and losses, claims and loss expenses payable	0	0
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	0	0
Deferred income	0	0
Deferred income taxes, net	0	0
Related party liabilities	(42,307)	(41,581)
Total liabilities	(42,307)	(41,581)
Stockholders' equity:
Additional paid-in capital	(117,601)	(117,601)
Accumulated other comprehensive loss	149,531	(102,633)
Retained earnings	(523,562)	(509,841)
Total stockholders' equity	(497,433)	(735,876)
Total liabilities and stockholders' equity	(539,740)	(777,457)
Consolidation, Eliminations [Member] | Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0	0
Consolidation, Eliminations [Member] | Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	0	0
Consolidation, Eliminations [Member] | Series A Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Consolidation, Eliminations [Member] | Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value, issued	0	0
Consolidation, Eliminations [Member] | Serial Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0	0
Consolidation, Eliminations [Member] | Amerco Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	(5,801)	(5,801)
Consolidation, Eliminations [Member] | Common Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	0	0
Consolidation, Eliminations [Member] | Preferred Stock in Treasury [Member]
Stockholders' equity:
Treasury stock, value	$ 0	$ 0