Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021
ASSETS:
Cash and cash equivalents	$ 3,098,271	$ 2,704,137	$ 1,519,981	$ 1,194,012
Reinsurance recoverables and trade receivables, net	219,574	229,343
Inventories, net	164,579	158,888
Prepaid expenses	231,714	236,915
Investments, fixed maturities and marketable equities	2,669,986	2,893,399
Investments, other	557,124	543,755
Deferred policy acquisition costs, net	129,568	103,828
Other assets	53,477	60,409
Right of use Assets - Financing	568,223	620,824
Right of use Assets - Operating	72,538	74,382
Related party assets	45,190	47,851
Subtotal assets	7,810,244	7,673,731
Investments in subsidiaries	0	0
Property, plant and equipment, at cost:
Land	1,354,587	1,283,142
Buildings and improvements	6,154,373	5,974,639
Furniture and equipment	858,094	846,132
Property, plant and equipment (gross)	13,912,488	13,358,406
Less: Accumulated depreciation	(3,891,128)	(3,732,556)
Total property, plant and equipment	10,021,360	9,625,850
Total assets	17,831,604	17,299,581	15,114,882
Liabilities:
Accounts payable and accrued expenses	722,617	677,785
Notes, loans and leases payable	6,232,564	6,022,497
Financing lease liability	312,411
Operating lease liability	72,277	74,197
Policy benefits and losses, claims and loss expenses payable	988,030	978,254
Liabilities from investment contracts	2,374,250	2,336,238
Other policyholders' funds and liabilities	11,999	10,812
Deferred income	63,647	49,157
Deferred income taxes, net	1,292,369	1,265,358
Related party liabilities	0	0
Total liabilities	11,757,753	11,414,298
Stockholders' equity:
Additional paid-in capital	453,819	453,819
Accumulated other comprehensive loss	(89,246)	46,384
Retained earnings	6,376,431	6,052,233
Total stockholders' equity	6,073,851	5,885,283
Total liabilities and stockholders' equity	17,831,604	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	671,880	615,679
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	4,873,554	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	2,982,541	2,643,213	1,455,973	1,010,275
Reinsurance recoverables and trade receivables, net	130,412	142,895
Inventories, net	164,579	158,888
Prepaid expenses	231,714	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	50,043	57,305
Right of use Assets - Financing	568,223	620,824
Right of use Assets - Operating	71,357	74,190
Related party assets	63,718	64,611
Subtotal assets	4,283,240	4,019,494
Investments in subsidiaries	606,813	737,073
Property, plant and equipment, at cost:
Land	1,354,587	1,283,142
Buildings and improvements	6,154,373	5,974,639
Furniture and equipment	858,094	846,132
Property, plant and equipment (gross)	13,912,488	13,358,406
Less: Accumulated depreciation	(3,891,128)	(3,732,556)
Total property, plant and equipment	10,021,360	9,625,850
Total assets	14,911,413	14,382,417
Liabilities:
Accounts payable and accrued expenses	712,167	663,482
Notes, loans and leases payable	6,232,564	6,022,497
Operating lease liability	71,083	73,998
Policy benefits and losses, claims and loss expenses payable	427,155	418,890
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	0	0
Deferred income	63,647	49,157
Deferred income taxes, net	1,306,768	1,244,639
Related party liabilities	26,918	25,668
Total liabilities	8,840,302	8,498,331
Stockholders' equity:
Additional paid-in capital	454,029	454,029
Accumulated other comprehensive loss	(91,986)	45,187
Retained earnings	6,376,221	6,052,023
Total stockholders' equity	6,071,111	5,884,086
Total liabilities and stockholders' equity	14,911,413	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	671,880	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	4,873,554	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	9,065	10,800	3,246	5,658
Reinsurance recoverables and trade receivables, net	52,491	50,235
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	282,715	297,488
Investments, other	116,696	114,269
Deferred policy acquisition costs, net	0	0
Other assets	480	371
Right of use Assets - Financing	0	0
Right of use Assets - Operating	1,101	93
Related party assets	6,964	6,713
Subtotal assets	469,512	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	469,512	479,969
Liabilities:
Accounts payable and accrued expenses	3,299	3,849
Notes, loans and leases payable	0	0
Operating lease liability	1,108	93
Policy benefits and losses, claims and loss expenses payable	159,142	160,379
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	3,362	3,521
Deferred income	0	0
Deferred income taxes, net	9,412	12,803
Related party liabilities	3,701	3,196
Total liabilities	180,024	183,841
Stockholders' equity:
Additional paid-in capital	91,120	91,120
Accumulated other comprehensive loss	3,394	16,630
Retained earnings	191,673	185,077
Total stockholders' equity	289,488	296,128
Total liabilities and stockholders' equity	469,512	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	106,665	50,124	60,762	178,079
Reinsurance recoverables and trade receivables, net	36,671	36,213
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	2,387,271	2,595,911
Investments, other	419,775	408,833
Deferred policy acquisition costs, net	129,568	103,828
Other assets	2,954	2,733
Right of use Assets - Financing	0	0
Right of use Assets - Operating	80	99
Related party assets	15,364	16,911
Subtotal assets	3,098,348	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	3,098,348	3,214,652
Liabilities:
Accounts payable and accrued expenses	7,151	10,454
Notes, loans and leases payable	0	0
Operating lease liability	86	106
Policy benefits and losses, claims and loss expenses payable	401,733	398,985
Liabilities from investment contracts	2,374,250	2,336,238
Other policyholders' funds and liabilities	8,637	7,291
Deferred income	0	0
Deferred income taxes, net	(23,811)	7,916
Related party liabilities	12,977	12,717
Total liabilities	2,781,023	2,773,707
Stockholders' equity:
Additional paid-in capital	26,271	26,271
Accumulated other comprehensive loss	(37,490)	87,200
Retained earnings	326,044	324,974
Total stockholders' equity	317,325	440,945
Total liabilities and stockholders' equity	3,098,348	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	$ 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	(40,856)	(40,384)
Subtotal assets	(40,856)	(40,384)
Investments in subsidiaries	(606,813)	(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	(647,669)	(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	(43,596)	(41,581)
Total liabilities	(43,596)	(41,581)
Stockholders' equity:
Additional paid-in capital	(117,601)	(117,601)
Accumulated other comprehensive loss	36,836	(102,633)
Retained earnings	(517,507)	(509,841)
Total stockholders' equity	(604,073)	(735,876)
Total liabilities and stockholders' equity	(647,669)	(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