Commitments and Contingencies - Commitments and Guarantees (Details) - USD ($) $ in Millions	Mar. 31, 2025	Mar. 31, 2024
Commitments:
Credit facilities commitments with dealers	$ 3,643	$ 3,244
Commitments under operating lease agreements	228	106
Total commitments	3,871	3,350
Total commitments and guarantees	3,971	3,450
Performance Guarantee [Member] \| Putnam and Gibson Counties [Member]
Commitments:
Guarantees of affiliate pollution control and solid waste disposal bonds	$ 100	$ 100

Commitments:

No definition available.

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- Definition

Amount of commitments the company entered into.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Aggregate amount of commitments and guarantor obligations.

+ References

No definition available.

+ Details

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Balance Type:	credit
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- Definition

Amount of credit facilities commitments with vehicle dealers.

+ References

No definition available.

+ Details

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Namespace Prefix:	ck0000834071_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-6

+ Details

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Balance Type:	credit
Period Type:	instant

- Details

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- Details

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