Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
ASSETS:
Cash and cash equivalents	$ 2,510,619	$ 2,704,137
Reinsurance recoverables and trade receivables, net	208,182	229,343
Inventories, net	150,140	158,888
Prepaid expenses	228,260	236,915
Investments, fixed maturities and marketable equities	2,723,201	2,893,399
Investments, other	518,455	543,755
Deferred policy acquisition costs, net	159,924	103,828
Other assets	57,272	60,409
Right of use Assets - Financing	504,640	620,824
Right of use Assets - Operating	63,856	74,382
Related party assets	75,549	47,851
Subtotal assets	7,200,098	7,673,731
Investments in subsidiaries	0	0
Property, plant and equipment, at cost:
Land	1,504,507	1,283,142
Buildings and improvements	6,728,424	5,974,639
Furniture and equipment	898,468	846,132
Property, plant and equipment (gross)	15,082,961	13,358,406
Less: Accumulated depreciation	(4,166,731)	(3,732,556)
Total property, plant and equipment	10,916,230	9,625,850
Total assets	18,116,328	17,299,581	$ 16,588,078
Liabilities:
Accounts payable and accrued expenses	703,412	677,785
Notes, loans and leases payable	6,200,397	6,022,497
Financing lease liability	252,102
Operating lease liability	63,402	74,197
Policy benefits and losses, claims and loss expenses payable	980,200	978,254
Liabilities from investment contracts	2,396,702	2,336,238
Other policyholders' funds and liabilities	12,579	10,812
Deferred income	45,222	49,157
Deferred income taxes, net	1,301,037	1,265,358
Related party liabilities	0	0
Total liabilities	11,702,951	11,414,298
Stockholders' equity:
Common stock, value, issued	176
Additional paid-in capital	453,643	453,819
Accumulated other comprehensive loss	(284,116)	46,384
Retained earnings	6,910,827	6,052,233
Total stockholders' equity	6,413,377	5,885,283
Total liabilities and stockholders' equity	18,116,328	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	784,394	615,679
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	5,167,168	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
Nonvoting Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	176	0
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	2,429,943	2,643,213
Reinsurance recoverables and trade receivables, net	124,001	142,895
Inventories, net	150,140	158,888
Prepaid expenses	228,260	236,915
Investments, fixed maturities and marketable equities	225,218	0
Investments, other	23,330	20,653
Deferred policy acquisition costs, net	0	0
Other assets	53,247	57,305
Right of use Assets - Financing	504,640	620,824
Right of use Assets - Operating	62,835	74,190
Related party assets	93,719	64,611
Subtotal assets	3,895,333	4,019,494
Investments in subsidiaries	422,549	737,073
Property, plant and equipment, at cost:
Land	1,504,507	1,283,142
Buildings and improvements	6,728,424	5,974,639
Furniture and equipment	898,468	846,132
Property, plant and equipment (gross)	15,082,961	13,358,406
Less: Accumulated depreciation	(4,166,731)	(3,732,556)
Total property, plant and equipment	10,916,230	9,625,850
Total assets	15,234,112	14,382,417
Liabilities:
Accounts payable and accrued expenses	690,320	663,482
Notes, loans and leases payable	6,200,397	6,022,497
Operating lease liability	62,367	73,998
Policy benefits and losses, claims and loss expenses payable	430,645	418,890
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	0	0
Deferred income	45,222	49,157
Deferred income taxes, net	1,372,516	1,244,639
Related party liabilities	24,866	25,668
Total liabilities	8,826,333	8,498,331
Stockholders' equity:
Common stock, value, issued	176
Additional paid-in capital	453,853	454,029
Accumulated other comprehensive loss	(289,714)	45,187
Retained earnings	6,910,617	6,052,023
Total stockholders' equity	6,407,779	5,884,086
Total liabilities and stockholders' equity	15,234,112	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	784,394	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	5,167,168	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	20,505	10,800
Reinsurance recoverables and trade receivables, net	51,481	50,235
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	267,338	297,488
Investments, other	108,440	114,269
Deferred policy acquisition costs, net	0	0
Other assets	507	371
Right of use Assets - Financing	0	0
Right of use Assets - Operating	977	93
Related party assets	3,998	6,713
Subtotal assets	453,246	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	453,246	479,969
Liabilities:
Accounts payable and accrued expenses	5,943	3,849
Notes, loans and leases payable	0	0
Operating lease liability	988	93
Policy benefits and losses, claims and loss expenses payable	156,259	160,379
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	4,154	3,521
Deferred income	0	0
Deferred income taxes, net	2,012	12,803
Related party liabilities	2,567	3,196
Total liabilities	171,923	183,841
Stockholders' equity:
Common stock, value, issued	0
Additional paid-in capital	91,120	91,120
Accumulated other comprehensive loss	(17,969)	16,630
Retained earnings	204,871	185,077
Total stockholders' equity	281,323	296,128
Total liabilities and stockholders' equity	453,246	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	60,171	50,124
Reinsurance recoverables and trade receivables, net	32,700	36,213
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	2,230,645	2,595,911
Investments, other	386,685	408,833
Deferred policy acquisition costs, net	159,924	103,828
Other assets	3,518	2,733
Right of use Assets - Financing	0	0
Right of use Assets - Operating	44	99
Related party assets	12,499	16,911
Subtotal assets	2,886,186	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	2,886,186	3,214,652
Liabilities:
Accounts payable and accrued expenses	7,149	10,454
Notes, loans and leases payable	0	0
Operating lease liability	47	106
Policy benefits and losses, claims and loss expenses payable	393,296	398,985
Liabilities from investment contracts	2,396,702	2,336,238
Other policyholders' funds and liabilities	8,425	7,291
Deferred income	0	0
Deferred income taxes, net	(73,491)	7,916
Related party liabilities	12,832	12,717
Total liabilities	2,744,960	2,773,707
Stockholders' equity:
Common stock, value, issued	0
Additional paid-in capital	26,271	26,271
Accumulated other comprehensive loss	(219,145)	87,200
Retained earnings	331,600	324,974
Total stockholders' equity	141,226	440,945
Total liabilities and stockholders' equity	2,886,186	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	(34,667)	(40,384)
Subtotal assets	(34,667)	(40,384)
Investments in subsidiaries	(422,549)	(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	(457,216)	(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	(40,265)	(41,581)
Total liabilities	(40,265)	(41,581)
Stockholders' equity:
Common stock, value, issued	0
Additional paid-in capital	(117,601)	(117,601)
Accumulated other comprehensive loss	242,712	(102,633)
Retained earnings	(536,261)	(509,841)
Total stockholders' equity	(416,951)	(735,876)
Total liabilities and stockholders' equity	(457,216)	(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