Finance Receivables - Summary of Finance Receivables (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Sep. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Mar. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables	$ 45,833		$ 37,946
Allowance for credit losses	(343)	$ (332)	(253)	$ (236)	$ (221)	$ (211)
Deferred dealer participation and other deferred costs	596		472
Unearned subsidy income	(551)		(580)
Finance receivables, net	45,535		37,585	35,817
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables	42,238		35,110
Allowance for credit losses	(336)	(327)	(248)	(231)	(216)	(206)
Deferred dealer participation and other deferred costs	596		472
Unearned subsidy income	(551)		(580)
Finance receivables, net	41,947		34,754
Dealer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables	3,595		2,836
Allowance for credit losses	(7)	$ (5)	(5)	$ (5)	$ (5)	$ (5)
Deferred dealer participation and other deferred costs	0		0
Unearned subsidy income	0		0
Finance receivables, net	$ 3,588		$ 2,831