Contingencies (Narratives) (Details) $ in Millions	12 Months Ended
Mar. 31, 2021 USD ($)
Covid 19 Pandemic
Unusual Or Infrequent Item Net Gain Loss [Abstract]
CARES act, refund estimate	$ 366.0

Amount of reasonable estimate for refund due to operating loss carrybacks, combined with depreciation adjustments pursuant to CARES act.

No definition available.

Name:	uhal_ReasonableEstimateRefundOperatingLossCarryback
Namespace Prefix:	uhal_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration