Related Party Transactions - Additional Information (Details) - USD ($) $ in Millions	Jun. 30, 2022	Mar. 31, 2022
Related Party Transactions [Abstract]
Subvention support receivable	$ 98	$ 66

For an unclassified balance sheet, amounts of subvention support due from parties associated with the reporting entity.

No definition available.

Name:	ck0000834071_SubventionSupportReceivableRelatedParties
Namespace Prefix:	ck0000834071_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant