Finance Receivables - Summary of Aging Analysis of Past Due Finance Receivables (Detail) - USD ($) $ in Millions	Dec. 31, 2025	Mar. 31, 2025
Financing Receivable, Past Due [Line Items]
Total finance receivables	$ 54,677	$ 52,912
Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	50,174	48,568
Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	40,028	38,529
Retail loans \| Used and certified automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	8,523	8,494
Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	1,623	1,545
Dealer loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	4,503	4,344
Dealer loans \| Wholesale flooring
Financing Receivable, Past Due [Line Items]
Total finance receivables	2,949	3,006
Dealer loans \| Commercial loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	1,554	1,338
Total past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	905	657
Total past due \| Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	904	656
Total past due \| Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	599	424
Total past due \| Retail loans \| Used and certified automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	260	203
Total past due \| Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	45	29
Total past due \| Dealer loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	1	1
Total past due \| Dealer loans \| Wholesale flooring
Financing Receivable, Past Due [Line Items]
Total finance receivables	1	1
Total past due \| Dealer loans \| Commercial loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
30 – 59 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	671	504
30 – 59 days past due \| Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	670	504
30 – 59 days past due \| Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	450	331
30 – 59 days past due \| Retail loans \| Used and certified automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	194	155
30 – 59 days past due \| Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	26	18
30 – 59 days past due \| Dealer loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	1	0
30 – 59 days past due \| Dealer loans \| Wholesale flooring
Financing Receivable, Past Due [Line Items]
Total finance receivables	1	0
30 – 59 days past due \| Dealer loans \| Commercial loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
60 – 89 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	185	118
60 – 89 days past due \| Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	185	118
60 – 89 days past due \| Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	120	73
60 – 89 days past due \| Retail loans \| Used and certified automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	53	38
60 – 89 days past due \| Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	12	7
60 – 89 days past due \| Dealer loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
60 – 89 days past due \| Dealer loans \| Wholesale flooring
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
60 – 89 days past due \| Dealer loans \| Commercial loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
90 days or greater past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	49	35
90 days or greater past due \| Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	49	34
90 days or greater past due \| Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	29	20
90 days or greater past due \| Retail loans \| Used and certified automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	13	10
90 days or greater past due \| Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	7	4
90 days or greater past due \| Dealer loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	1
90 days or greater past due \| Dealer loans \| Wholesale flooring
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	1
90 days or greater past due \| Dealer loans \| Commercial loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
Current or less than 30 days past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	53,772	52,255
Current or less than 30 days past due \| Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	49,270	47,912
Current or less than 30 days past due \| Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	39,429	38,105
Current or less than 30 days past due \| Retail loans \| Used and certified automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	8,263	8,291
Current or less than 30 days past due \| Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	1,578	1,516
Current or less than 30 days past due \| Dealer loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	4,502	4,343
Current or less than 30 days past due \| Dealer loans \| Wholesale flooring
Financing Receivable, Past Due [Line Items]
Total finance receivables	2,948	3,005
Current or less than 30 days past due \| Dealer loans \| Commercial loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	$ 1,554	$ 1,338