Finance Receivables - Summary of Aging Analysis of Past Due Finance Receivables (Detail) - USD ($) $ in Millions	Jun. 30, 2025	Mar. 31, 2025
Financing Receivable, Past Due [Line Items]
Total finance receivables	$ 54,709	$ 52,912
Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	50,124	48,568
Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	39,855	38,529
Retail loans \| Used and certified automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	8,645	8,494
Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	1,624	1,545
Dealer loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	4,585	4,344
Dealer loans \| Wholesale flooring
Financing Receivable, Past Due [Line Items]
Total finance receivables	3,203	3,006
Dealer loans \| Commercial loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	1,382	1,338
Total past due
Financing Receivable, Past Due [Line Items]
Total finance receivables	737	657
Total past due \| Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	736	656
Total past due \| Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	476	424
Total past due \| Retail loans \| Used and certified automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	228	203
Total past due \| Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	32	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	544	504
30 – 59 days past due \| Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	544	504
30 – 59 days past due \| Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	356	331
30 – 59 days past due \| Retail loans \| Used and certified automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	168	155
30 – 59 days past due \| Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	20	18
30 – 59 days past due \| Dealer loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	0
30 – 59 days past due \| Dealer loans \| Wholesale flooring
Financing Receivable, Past Due [Line Items]
Total finance receivables	0	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	156	118
60 – 89 days past due \| Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	155	118
60 – 89 days past due \| Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	98	73
60 – 89 days past due \| Retail loans \| Used and certified automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	49	38
60 – 89 days past due \| Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	8	7
60 – 89 days past due \| Dealer loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	1	0
60 – 89 days past due \| Dealer loans \| Wholesale flooring
Financing Receivable, Past Due [Line Items]
Total finance receivables	1	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	37	35
90 days or greater past due \| Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	37	34
90 days or greater past due \| Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	22	20
90 days or greater past due \| Retail loans \| Used and certified automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	11	10
90 days or greater past due \| Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	4	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	53,972	52,255
Current or less than 30 days past due \| Retail loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	49,388	47,912
Current or less than 30 days past due \| Retail loans \| New automobile
Financing Receivable, Past Due [Line Items]
Total finance receivables	39,379	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	8,417	8,291
Current or less than 30 days past due \| Retail loans \| Motorcycle and other
Financing Receivable, Past Due [Line Items]
Total finance receivables	1,592	1,516
Current or less than 30 days past due \| Dealer loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	4,584	4,343
Current or less than 30 days past due \| Dealer loans \| Wholesale flooring
Financing Receivable, Past Due [Line Items]
Total finance receivables	3,202	3,005
Current or less than 30 days past due \| Dealer loans \| Commercial loans
Financing Receivable, Past Due [Line Items]
Total finance receivables	$ 1,382	$ 1,338