Finance Receivables, Net - Net Financing Receivables (Details) - USD ($) $ in Millions	Sep. 30, 2021	Mar. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables	$ 80,739	$ 80,370
Allowance for credit losses	(1,190)	(1,178)
Finance receivables, net	79,549	79,192
Finance Receivables, Net [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables	80,758	80,633
Deferred origination costs	1,266	1,145
Deferred income	(1,285)	(1,408)
Allowance for credit losses	(1,190)	(1,178)
Finance receivables, net	79,549	79,192
Finance Receivables, Net [Member] | Retail receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables	70,808	66,991
Finance Receivables, Net [Member] | Dealer financing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables	9,950	13,642
Allowance for credit losses	(55)	(103)
Finance Receivables, Net [Member] | Retail and securitized retail receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	$ (1,135)	$ (1,075)