Allowance for Credit Losses - Additional Information (Details) - Finance Receivables, Net [Member] - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable Allowance For Credit Losses [Line Items]
Ending balance: Collectively evaluated for impairment	$ 70,049	$ 67,983
Retail and Commercial Loan [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Impaired finance receivables aggregated and collectively evaluated for impairment	216	220
Dealer Products [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Ending balance: Collectively evaluated for impairment	16,092	15,828
TMNA [Member] | Financial Guarantee [Member] | Dealer Products [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Ending balance: Collectively evaluated for impairment	1,054	1,086
Private Toyota Distributors [Member] | Financial Guarantee [Member] | Dealer Products [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Ending balance: Collectively evaluated for impairment	$ 137	$ 175