Finance Receivables - Summary of Aging Analysis of Past Due Finance Receivables (Detail) - USD ($) $ in Millions	Jun. 30, 2026	Mar. 31, 2026
Financing Receivable, Past Due [Line Items]
Total finance receivables	$ 55,338	$ 54,779
Total past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	813	758
30 – 59 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	607	590
60 – 89 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	166	133
90 days or greater past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	40	35
Current or less than 30 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	54,525	54,021
Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	50,642	50,076
Retail loans \| Total past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	813	758
Retail loans \| 30 – 59 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	607	590
Retail loans \| 60 – 89 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	166	133
Retail loans \| 90 days or greater past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	40	35
Retail loans \| Current or less than 30 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	49,829	49,318
Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	40,401	39,918
Retail loans \| New automobile \| Total past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	553	513
Retail loans \| New automobile \| 30 – 59 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	415	402
Retail loans \| New automobile \| 60 – 89 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	112	89
Retail loans \| New automobile \| 90 days or greater past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	26	22
Retail loans \| New automobile \| Current or less than 30 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	39,848	39,405
Retail loans \| Used and certified automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	8,647	8,568
Retail loans \| Used and certified automobile \| Total past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	222	208
Retail loans \| Used and certified automobile \| 30 – 59 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	169	165
Retail loans \| Used and certified automobile \| 60 – 89 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	44	35
Retail loans \| Used and certified automobile \| 90 days or greater past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	9	8
Retail loans \| Used and certified automobile \| Current or less than 30 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	8,425	8,360
Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	1,594	1,590
Retail loans \| Motorcycle and other \| Total past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	38	37
Retail loans \| Motorcycle and other \| 30 – 59 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	23	23
Retail loans \| Motorcycle and other \| 60 – 89 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	10	9
Retail loans \| Motorcycle and other \| 90 days or greater past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	5	5
Retail loans \| Motorcycle and other \| Current or less than 30 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	1,556	1,553
Dealer loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	4,696	4,703
Dealer loans \| Total past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Dealer loans \| 30 – 59 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Dealer loans \| 60 – 89 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Dealer loans \| 90 days or greater past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Dealer loans \| Current or less than 30 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	4,696	4,703
Dealer loans \| Wholesale flooring
Financing Receivable, Past Due [Line Items]
Total finance receivables	3,062	3,136
Dealer loans \| Wholesale flooring \| Total past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Dealer loans \| Wholesale flooring \| 30 – 59 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Dealer loans \| Wholesale flooring \| 60 – 89 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Dealer loans \| Wholesale flooring \| 90 days or greater past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Dealer loans \| Wholesale flooring \| Current or less than 30 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	3,062	3,136
Dealer loans \| Commercial loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	1,634	1,567
Dealer loans \| Commercial loans \| Total past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Dealer loans \| Commercial loans \| 30 – 59 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Dealer loans \| Commercial loans \| 60 – 89 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Dealer loans \| Commercial loans \| 90 days or greater past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Dealer loans \| Commercial loans \| Current or less than 30 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	$ 1,634	$ 1,567