Consolidating financial information by industry segment (Balance Sheets) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020
ASSETS:
Cash and cash equivalents	$ 1,519,981	$ 1,194,012	$ 825,074	$ 494,352
Reinsurance recoverables and trade receivables, net	233,056	224,426
Inventories, net	117,978	105,577
Prepaid expenses	306,565	469,144
Investments, fixed maturities and marketable equities	2,755,133	2,695,656
Investments, other	525,893	489,759
Deferred policy acquisition costs, net	101,169	89,749
Other assets	46,910	47,730
Right of use Assets - Financing	814,875	877,038
Right of use Assets - Operating	89,369	92,505
Related party assets	34,481	35,395
Subtotal assets	6,545,410	6,320,991
Investments in subsidiaries	0	0
Property, plant and equipment, at cost:
Land	1,110,300	1,075,813
Buildings and improvements	5,284,224	5,163,705
Furniture and equipment	796,077	786,505
Property, plant and equipment (gross)	11,805,268	11,413,668
Less: Accumulated depreciation	(3,235,796)	(3,083,053)
Total property, plant and equipment	8,569,472	8,330,615
Total assets	15,114,882	14,651,606	13,712,359
Liabilities:
Accounts payable and accrued expenses	696,797	645,575
Notes, loans and leases payable	4,673,383	4,668,907
Financing lease liability	468,484
Operating lease liability	89,390	92,510
Policy benefits and losses, claims and loss expenses payable	1,007,144	997,701
Liabilities from investment contracts	2,226,560	2,161,530
Other policyholders' funds and liabilities	10,989	12,420
Deferred income	54,738	42,592
Deferred income taxes, net	1,244,353	1,178,489
Related party liabilities	0	0
Total liabilities	10,003,354	9,799,724
Stockholders' equity:
Additional paid-in capital	453,819	453,819
Accumulated other comprehensive loss	31,132	106,857
Retained earnings	5,293,730	4,958,359
Total stockholders' equity	5,111,528	4,851,882
Total liabilities and stockholders' equity	15,114,882	14,651,606
Rental Trailers and Other Rental Equipment [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	495,012	477,921
Rental Trucks [Member]
Property, plant and equipment, at cost:
Property subject to or available for operating lease, gross	4,119,655	3,909,724
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	1,455,973	1,010,275	770,941	459,078
Reinsurance recoverables and trade receivables, net	120,946	118,741
Inventories, net	117,978	105,577
Prepaid expenses	306,565	469,144
Investments, fixed maturities and marketable equities	0	0
Investments, other	20,733	20,733
Deferred policy acquisition costs, net	0	0
Other assets	43,439	44,763
Right of use Assets - Financing	814,875	877,038
Right of use Assets - Operating	89,034	92,245
Related party assets	53,783	54,042
Subtotal assets	3,023,326	2,792,558
Investments in subsidiaries	677,909	741,860
Property, plant and equipment, at cost:
Land	1,110,300	1,075,813
Buildings and improvements	5,284,224	5,163,705
Furniture and equipment	796,077	786,505
Property, plant and equipment (gross)	11,805,268	11,413,668
Less: Accumulated depreciation	(3,235,796)	(3,083,053)
Total property, plant and equipment	8,569,472	8,330,615
Total assets	12,270,707	11,865,033
Liabilities:
Accounts payable and accrued expenses	679,461	636,257
Notes, loans and leases payable	4,662,325	4,657,720
Operating lease liability	89,042	92,236
Policy benefits and losses, claims and loss expenses payable	433,394	427,073
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	0	0
Deferred income	54,738	42,592
Deferred income taxes, net	1,217,716	1,136,149
Related party liabilities	26,836	25,413
Total liabilities	7,163,512	7,017,440
Stockholders' equity:
Additional paid-in capital	454,029	454,029
Accumulated other comprehensive loss	26,799	102,568
Retained earnings	5,293,520	4,958,149
Total stockholders' equity	5,107,195	4,847,593
Total liabilities and stockholders' equity	12,270,707	11,865,033
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	495,012	477,921
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	4,119,655	3,909,724
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	3,246	5,658	4,119	4,794
Reinsurance recoverables and trade receivables, net	67,589	67,069
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	290,571	295,753
Investments, other	94,028	90,412
Deferred policy acquisition costs, net	0	0
Other assets	829	436
Right of use Assets - Financing	0	0
Right of use Assets - Operating	184	92
Related party assets	6,557	6,854
Subtotal assets	463,004	466,274
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	463,004	466,274
Liabilities:
Accounts payable and accrued expenses	2,260	2,029
Notes, loans and leases payable	0	0
Operating lease liability	188	96
Policy benefits and losses, claims and loss expenses payable	179,294	178,942
Liabilities from investment contracts	0	0
Other policyholders' funds and liabilities	3,237	3,698
Deferred income	0	0
Deferred income taxes, net	11,667	13,046
Related party liabilities	3,812	5,821
Total liabilities	200,458	203,632
Stockholders' equity:
Additional paid-in capital	91,120	91,120
Accumulated other comprehensive loss	15,148	22,546
Retained earnings	152,977	145,675
Total stockholders' equity	262,546	262,642
Total liabilities and stockholders' equity	463,004	466,274
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	60,762	178,079	50,014	30,480
Reinsurance recoverables and trade receivables, net	44,521	38,616
Inventories, net	0	0
Prepaid expenses	0	0
Investments, fixed maturities and marketable equities	2,464,562	2,399,903
Investments, other	411,132	378,614
Deferred policy acquisition costs, net	101,169	89,749
Other assets	2,642	2,531
Right of use Assets - Financing	0	0
Right of use Assets - Operating	151	168
Related party assets	13,797	13,850
Subtotal assets	3,098,736	3,101,510
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	3,098,736	3,101,510
Liabilities:
Accounts payable and accrued expenses	15,076	7,289
Notes, loans and leases payable	11,058	11,187
Operating lease liability	160	178
Policy benefits and losses, claims and loss expenses payable	394,456	391,686
Liabilities from investment contracts	2,226,560	2,161,530
Other policyholders' funds and liabilities	7,752	8,722
Deferred income	0	0
Deferred income taxes, net	14,970	29,294
Related party liabilities	13,341	12,406
Total liabilities	2,683,373	2,622,292
Stockholders' equity:
Additional paid-in capital	26,271	26,271
Accumulated other comprehensive loss	75,145	140,817
Retained earnings	311,447	309,630
Total stockholders' equity	415,363	479,218
Total liabilities and stockholders' equity	3,098,736	3,101,510
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	(39,656)	(39,351)
Subtotal assets	(39,656)	(39,351)
Investments in subsidiaries	(677,909)	(741,860)
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	(717,565)	(781,211)
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	(43,989)	(43,640)
Total liabilities	(43,989)	(43,640)
Stockholders' equity:
Additional paid-in capital	(117,601)	(117,601)
Accumulated other comprehensive loss	(85,960)	(159,074)
Retained earnings	(464,214)	(455,095)
Total stockholders' equity	(673,576)	(737,571)
Total liabilities and stockholders' equity	(717,565)	(781,211)
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