Related Party Transactions - Related Party Transactions Included in Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2025	Jun. 30, 2024
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	$ 320	$ 295
Expenses:
Operating and administrative	427	440
TMCC-affiliated companies [Member]
Net financing revenues:
Manufacturer's subvention and other revenues	270	225
Depreciation on operating leases	4	17
Interest expense:
Credit support fees, interest and other expenses	26	29
Voluntary protection contract revenues and insurance earned premiums:
Voluntary protection contract revenues and insurance earned premiums	52	41
Investment and other income, net:
Interest and other income	102	13
Expenses:
Operating and administrative	$ 29	$ 26