Finance Receivables, Net - Net Financing Receivables (Details) - USD ($) $ in Millions	Dec. 31, 2020	Mar. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables	$ 79,962	$ 74,961
Allowance for credit losses	(1,162)	(727)
Finance receivables, net	78,800	73,996
Finance Receivables, Net [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables	80,314	74,961
Deferred origination costs	1,083	890
Deferred income	(1,435)	(1,128)
Allowance for credit losses	(1,162)	(727)
Finance receivables, net	78,800	73,996
Finance Receivables, Net [Member] | Retail receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables	65,102	57,088
Finance Receivables, Net [Member] | Dealer financing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross finance receivables	15,212	17,873
Allowance for credit losses	(110)	(241)
Finance Receivables, Net [Member] | Retail and securitized retail receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	$ (1,052)	$ (486)