Commitments and Contingencies - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022
Commitments And Contingencies Disclosure [Line Items]
Lease expense under operating leases	$ 2	$ 2	$ 7	$ 7
Operating lease, weighted average remaining lease term	7 years 9 months 18 days		7 years 9 months 18 days
Operating lease, weighted average discount rate (percentage)	3.00%		3.00%
Revolving lines of credit
Commitments And Contingencies Disclosure [Line Items]
Unused balance of commercial revolving lines of credit	$ 425		$ 425
Construction of auto dealership facilities
Commitments And Contingencies Disclosure [Line Items]
Remaining unfunded balance for construction loans	$ 9		$ 9