Commitments and Contingencies - Commitments and Guarantees (Details) - USD ($) $ in Millions	Mar. 31, 2023	Mar. 31, 2022
Commitments:
Credit facilities commitments with dealers	$ 3,153	$ 3,289
Commitments under operating lease agreements	106	119
Total commitments	3,259	3,408
Total commitments and guarantees	3,359	3,508
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

Name:	ck0000834071_Commitments
Namespace Prefix:	ck0000834071_
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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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of credit facilities commitments with vehicle dealers.

+ References

No definition available.

+ Details

Name:	ck0000834071_CreditFacilitiesCommitmentsWithVehicleDealers
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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI https://asc.fasb.org/extlink&oid=124440162&loc=d3e12069-110248

+ 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 6
-URI https://asc.fasb.org/extlink&oid=128292326&loc=SL77918701-209980

+ Details

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Balance Type:	credit
Period Type:	instant

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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