Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022
ASSETS:
Cash and cash equivalents	$ 2,377,124	$ 2,060,524
Reinsurance recoverables and trade receivables, net	206,663	189,498
Inventories, net	164,884	151,474
Prepaid expenses	232,039	241,711
Investments, fixed maturities and marketable equities	2,469,512	2,770,394
Investments, other	620,140	575,540
Deferred policy acquisition costs, net	123,596	128,463
Other assets	60,821	51,052
Right of use Assets - Financing	420,496	474,765
Right of use Assets - Operating	59,496	58,917
Related party assets	43,102	48,308
Subtotal assets	6,777,873	6,750,646
Investments in subsidiaries	0	0
Property, plant and equipment, at cost:
Land	1,555,326	1,537,206
Buildings and improvements	7,364,517	7,088,810
Furniture and equipment	942,036	928,241
Property, plant and equipment (gross)	16,322,927	15,660,293
Less: Accumulated depreciation	(4,486,766)	(4,310,205)
Total property, plant and equipment	11,836,161	11,350,088
Total assets	18,614,034	18,100,734	$ 17,793,811
Liabilities:
Accounts payable and accrued expenses	778,605	761,039
Notes, loans and leases payable	6,287,231	6,108,042
Financing lease liability	189,037
Operating lease liability	58,808	58,373
Policy benefits and losses, claims and loss expenses payable	878,436	880,202
Liabilities from investment contracts	2,384,330	2,398,884
Other policyholders' funds and liabilities	12,218	8,232
Deferred income	64,790	52,282
Deferred income taxes, net	1,371,859	1,329,489
Related party liabilities	0	0
Total liabilities	11,836,277	11,596,543
Stockholders' equity:
Additional paid-in capital	453,643	453,643
Accumulated other comprehensive loss	(261,836)	(285,623)
Retained earnings	7,252,927	7,003,148
Total stockholders' equity	6,777,757	6,504,191
Total liabilities and stockholders' equity	18,614,034	18,100,734
Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	866,916	827,696
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	5,594,132	5,278,340
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	2,302,380	2,034,242
Reinsurance recoverables and trade receivables, net	125,222	107,823
Inventories, net	164,884	151,474
Prepaid expenses	232,039	241,711
Investments, fixed maturities and marketable equities	0	227,737
Investments, other	23,330	23,314
Deferred policy acquisition costs, net	0	0
Other assets	54,916	46,438
Right of use Assets - Financing	420,496	474,765
Right of use Assets - Operating	58,622	57,978
Related party assets	65,625	69,144
Subtotal assets	3,447,514	3,434,626
Investments in subsidiaries	459,095	426,779
Property, plant and equipment, at cost:
Land	1,555,326	1,537,206
Buildings and improvements	7,364,517	7,088,810
Furniture and equipment	942,036	928,241
Property, plant and equipment (gross)	16,322,927	15,660,293
Less: Accumulated depreciation	(4,486,766)	(4,310,205)
Total property, plant and equipment	11,836,161	11,350,088
Total assets	15,742,770	15,211,493
Liabilities:
Accounts payable and accrued expenses	768,784	729,679
Notes, loans and leases payable	6,287,231	6,108,042
Operating lease liability	57,937	57,418
Policy benefits and losses, claims and loss expenses payable	328,009	335,227
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	0	0
Deferred income	64,790	52,282
Deferred income taxes, net	1,437,773	1,405,391
Related party liabilities	26,630	25,082
Total liabilities	8,971,154	8,713,121
Stockholders' equity:
Additional paid-in capital	453,853	453,853
Accumulated other comprehensive loss	(267,977)	(291,442)
Retained earnings	7,252,717	7,002,938
Total stockholders' equity	6,771,616	6,498,372
Total liabilities and stockholders' equity	15,742,770	15,211,493
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	866,916	827,696
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	5,594,132	5,278,340
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	14,038	11,276
Reinsurance recoverables and trade receivables, net	49,051	48,344
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	274,003	271,156
Investments, other	129,392	125,130
Deferred policy acquisition costs, net	0	0
Other assets	1,063	730
Right of use Assets - Financing	0	0
Right of use Assets - Operating	850	914
Related party assets	2,860	2,347
Subtotal assets	471,257	459,897
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	471,257	459,897
Liabilities:
Accounts payable and accrued expenses	3,303	4,470
Notes, loans and leases payable	0	0
Operating lease liability	864	928
Policy benefits and losses, claims and loss expenses payable	148,960	153,007
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	2,435	2,702
Deferred income	0	0
Deferred income taxes, net	4,776	1,713
Related party liabilities	3,199	2,544
Total liabilities	163,537	165,364
Stockholders' equity:
Additional paid-in capital	91,120	91,120
Accumulated other comprehensive loss	(11,043)	(14,720)
Retained earnings	224,342	214,832
Total stockholders' equity	307,720	294,533
Total liabilities and stockholders' equity	471,257	459,897
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	60,706	15,006
Reinsurance recoverables and trade receivables, net	32,390	33,331
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	2,195,509	2,271,501
Investments, other	467,418	427,096
Deferred policy acquisition costs, net	123,596	128,463
Other assets	4,842	3,884
Right of use Assets - Financing	0	0
Right of use Assets - Operating	24	25
Related party assets	11,945	12,268
Subtotal assets	2,896,430	2,891,574
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	2,896,430	2,891,574
Liabilities:
Accounts payable and accrued expenses	6,518	26,890
Notes, loans and leases payable	0	0
Operating lease liability	7	27
Policy benefits and losses, claims and loss expenses payable	401,467	391,968
Liabilities from investment contracts	2,384,330	2,398,884
Other policyholders' funds and liabilities	9,783	5,530
Deferred income	0	0
Deferred income taxes, net	(70,690)	(77,615)
Related party liabilities	13,640	13,644
Total liabilities	2,745,055	2,759,328
Stockholders' equity:
Additional paid-in capital	26,271	26,271
Accumulated other comprehensive loss	(207,495)	(225,904)
Retained earnings	330,099	329,379
Total stockholders' equity	151,375	132,246
Total liabilities and stockholders' equity	2,896,430	2,891,574
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	(37,328)	(35,451)
Subtotal assets	(37,328)	(35,451)
Investments in subsidiaries	(459,095)	(426,779)
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	(496,423)	(462,230)
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	(43,469)	(41,270)
Total liabilities	(43,469)	(41,270)
Stockholders' equity:
Additional paid-in capital	(117,601)	(117,601)
Accumulated other comprehensive loss	224,679	246,443
Retained earnings	(554,231)	(544,001)
Total stockholders' equity	(452,954)	(420,960)
Total liabilities and stockholders' equity	(496,423)	(462,230)
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