Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Mar. 31, 2023	Sep. 30, 2022
ASSETS:
Cash and cash equivalents	$ 2,145,131	$ 2,060,524
Reinsurance recoverables and trade receivables, net	212,565	189,498
Inventories, net	161,535	151,474
Prepaid expenses	263,541	241,711
Investments, fixed maturities and marketable equities	2,534,164	2,770,394
Investments, other	650,151	575,540
Deferred policy acquisition costs, net	121,365	128,463
Other assets	52,769	51,052
Right of use Assets - Financing	377,733	474,765
Right of use Assets - Operating	65,316	58,917
Related Parties Amounts Due	40,140	48,308
Subtotal assets	6,624,410	6,750,646
Investments in subsidiaries	0	0
Property, plant and equipment, at cost:
Land	1,613,871	1,537,206
Buildings and improvements	7,649,849	7,088,810
Furniture and equipment	966,211	928,241
Property, plant and equipment (gross)	17,063,484	15,660,293
Less: Accumulated depreciation	(4,666,444)	(4,310,205)
Total property, plant and equipment	12,397,040	11,350,088
Total assets	19,021,450	18,100,734	$ 18,143,343
Liabilities:
Accounts payable and accrued expenses	757,988	761,039
Notes, loans and leases payable	6,400,899	6,108,042
Operating lease liability	64,580	58,373
Policy benefits and losses, claims and loss expenses payable	865,397	880,202
Liabilities from investment contracts	2,393,590	2,398,884
Other policyholders' funds and liabilities	7,677	8,232
Deferred income	56,821	52,282
Deferred income taxes, net	1,444,120	1,329,489
Related party liabilities	0	0
Total liabilities	11,991,072	11,596,543
Stockholders' equity:
Common stock, value, issued		176
Additional paid-in capital	453,643	453,643
Accumulated other comprehensive loss	(275,664)	(285,623)
Retained earnings	7,519,376	7,003,148
Total stockholders' equity	7,030,378	6,504,191
Total liabilities and stockholders' equity	19,021,450	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	912,046	827,696
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	5,921,507	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
Nonvoting Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	176	176
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	2,068,790	2,034,242
Reinsurance recoverables and trade receivables, net	130,372	107,823
Inventories, net	161,535	151,474
Prepaid expenses	263,541	241,711
Investments, fixed maturities and marketable equities	97,372	227,737
Investments, other	23,330	23,314
Deferred policy acquisition costs, net	0	0
Other assets	46,667	46,438
Right of use Assets - Financing	377,733	474,765
Right of use Assets - Operating	64,378	57,978
Related Parties Amounts Due	62,931	69,144
Subtotal assets	3,296,649	3,434,626
Investments in subsidiaries	462,493	426,779
Property, plant and equipment, at cost:
Land	1,613,871	1,537,206
Buildings and improvements	7,649,849	7,088,810
Furniture and equipment	966,211	928,241
Property, plant and equipment (gross)	17,063,484	15,660,293
Less: Accumulated depreciation	(4,666,444)	(4,310,205)
Total property, plant and equipment	12,397,040	11,350,088
Total assets	16,156,182	15,211,493
Liabilities:
Accounts payable and accrued expenses	745,606	729,679
Notes, loans and leases payable	6,400,899	6,108,042
Operating lease liability	63,627	57,418
Policy benefits and losses, claims and loss expenses payable	324,642	335,227
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	0	0
Deferred income	56,821	52,282
Deferred income taxes, net	1,514,732	1,405,391
Related party liabilities	25,754	25,082
Total liabilities	9,132,081	8,713,121
Stockholders' equity:
Common stock, value, issued		176
Additional paid-in capital	453,853	453,853
Accumulated other comprehensive loss	(281,941)	(291,442)
Retained earnings	7,519,166	7,002,938
Total stockholders' equity	7,024,101	6,498,372
Total liabilities and stockholders' equity	16,156,182	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	912,046	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	5,921,507	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] | Nonvoting Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	176
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	44,272	11,276
Reinsurance recoverables and trade receivables, net	50,525	48,344
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	268,769	271,156
Investments, other	115,583	125,130
Deferred policy acquisition costs, net	0	0
Other assets	800	730
Right of use Assets - Financing	0	0
Right of use Assets - Operating	785	914
Related Parties Amounts Due	1,223	2,347
Subtotal assets	481,957	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	481,957	459,897
Liabilities:
Accounts payable and accrued expenses	4,472	4,470
Notes, loans and leases payable	0	0
Operating lease liability	800	928
Policy benefits and losses, claims and loss expenses payable	150,148	153,007
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	2,126	2,702
Deferred income	0	0
Deferred income taxes, net	3,973	1,713
Related party liabilities	2,969	2,544
Total liabilities	164,488	165,364
Stockholders' equity:
Common stock, value, issued		0
Additional paid-in capital	91,120	91,120
Accumulated other comprehensive loss	(13,532)	(14,720)
Retained earnings	236,580	214,832
Total stockholders' equity	317,469	294,533
Total liabilities and stockholders' equity	481,957	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] | Nonvoting Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0
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	32,069	15,006
Reinsurance recoverables and trade receivables, net	31,668	33,331
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	2,168,023	2,271,501
Investments, other	511,238	427,096
Deferred policy acquisition costs, net	121,365	128,463
Other assets	5,302	3,884
Right of use Assets - Financing	0	0
Right of use Assets - Operating	153	25
Related Parties Amounts Due	11,808	12,268
Subtotal assets	2,881,626	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	2,881,626	2,891,574
Liabilities:
Accounts payable and accrued expenses	7,910	26,890
Notes, loans and leases payable	0	0
Operating lease liability	153	27
Policy benefits and losses, claims and loss expenses payable	390,607	391,968
Liabilities from investment contracts	2,393,590	2,398,884
Other policyholders' funds and liabilities	5,551	5,530
Deferred income	0	0
Deferred income taxes, net	(74,585)	(77,615)
Related party liabilities	13,376	13,644
Total liabilities	2,736,602	2,759,328
Stockholders' equity:
Common stock, value, issued		0
Additional paid-in capital	26,271	26,271
Accumulated other comprehensive loss	(218,470)	(225,904)
Retained earnings	334,723	329,379
Total stockholders' equity	145,024	132,246
Total liabilities and stockholders' equity	2,881,626	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] | Nonvoting Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0
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 Parties Amounts Due	(35,822)	(35,451)
Subtotal assets	(35,822)	(35,451)
Investments in subsidiaries	(462,493)	(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	(498,315)	(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	(42,099)	(41,270)
Total liabilities	(42,099)	(41,270)
Stockholders' equity:
Common stock, value, issued		0
Additional paid-in capital	(117,601)	(117,601)
Accumulated other comprehensive loss	238,279	246,443
Retained earnings	(571,093)	(544,001)
Total stockholders' equity	(456,216)	(420,960)
Total liabilities and stockholders' equity	(498,315)	(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] | Nonvoting Common Stock [Member]
Stockholders' equity:
Common stock, value, issued	0
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