Finance Receivables, Net - Net Financing Receivables (Details) - USD ($)	Mar. 31, 2021	Mar. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables	$ 80,370,000,000	$ 74,961,000,000
Allowance for credit losses	(1,178)	(727)
Finance receivables, net	79,192,000,000	73,996,000,000
Dealer financing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables		17,873,000,000
Finance Receivables, Net [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables	80,633,000,000	74,961,000,000
Deferred origination costs	1,145,000,000	890,000,000
Deferred income	(1,408,000,000)	(1,128,000,000)
Allowance for credit losses	(1,178,000,000)	(727,000,000)
Finance receivables, net	79,192,000,000	73,996,000,000
Finance Receivables, Net [Member] | Retail receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables	66,991,000,000	57,088,000,000
Finance Receivables, Net [Member] | Dealer financing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables	13,642,000,000	17,873,000,000
Allowance for credit losses	(103,000,000)	(241,000,000)
Finance Receivables, Net [Member] | Retail and securitized retail receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	$ (1,075,000,000)	$ (486,000,000)