Finance Receivables - Summary of Loans by Risk Rate Grouping (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Mar. 31, 2025
Current Period
Total	$ 54,887		$ 53,042
Current Period, Gross charge-offs
Total	102	$ 79
Prior Year
Total	54,887		53,042
Prior Period, Gross charge-offs
Total	102	79
Dealer loans
Current Period
Total	4,585		4,344
Current Period, Gross charge-offs
Total	0	0
Prior Year
Total	4,585		4,344
Prior Period, Gross charge-offs
Total	0	$ 0
Dealer loans \| Performing
Current Period
Total	4,585		4,344
Current Period, Gross charge-offs
Total	0		0
Prior Year
Total	4,585		4,344
Prior Period, Gross charge-offs
Total	0		0
Dealer loans \| Group I \| Performing
Current Period
Total	3,144		2,989
Prior Year
Total	3,144		2,989
Dealer loans \| Group II \| Performing
Current Period
Total	1,440		1,354
Prior Year
Total	1,440		1,354
Dealer loans \| Group III \| Performing
Current Period
Total	1		1
Prior Year
Total	1		1
Dealer loans \| Commercial loans \| Performing
Current Period
2026	16		172
2025	171		166
2024	164		55
2023	54		13
2022	13		92
Prior	162		78
Revolving loans	802		762
Current Period, Gross charge-offs
2026	0		0
2025	0		0
2024	0		0
2023	0		0
2022	0		0
Prior	0		0
Revolving loans	0		0
Prior Year
2025	16		172
2024	171		166
2023	164		55
2022	54		13
2021	13		92
Prior	162		78
Revolving loans	802		762
Prior Period, Gross charge-offs
2025	0		0
2024	0		0
2023	0		0
2022	0		0
2021	0		0
Prior	0		0
Revolving loans	0		0
Dealer loans \| Commercial loans \| Group I \| Performing
Current Period
2026	11		149
2025	147		110
2024	109		52
2023	52		13
2022	13		86
Prior	129		53
Revolving loans	802		762
Prior Year
2025	11		149
2024	147		110
2023	109		52
2022	52		13
2021	13		86
Prior	129		53
Revolving loans	802		762
Dealer loans \| Commercial loans \| Group II \| Performing
Current Period
2026	5		23
2025	24		56
2024	55		3
2023	2
2022	0		6
Prior	33		25
Revolving loans	0
Prior Year
2025	5		23
2024	24		56
2023	55		3
2022	2
2021	0		6
Prior	33		25
Revolving loans	0
Dealer loans \| Commercial loans \| Group III \| Performing
Current Period
2026	0
2025	0
2024	0
2023	0
2022	0
Prior	0
Revolving loans	0
Prior Year
2025	0
2024	0
2023	0
2022	0
2021	0
Prior	0
Revolving loans	0
Dealer loans \| Wholesale flooring \| Performing
Current Period
Total	3,203		3,006
Current Period, Gross charge-offs
Total	0		0
Prior Year
Total	3,203		3,006
Prior Period, Gross charge-offs
Total	0		0
Dealer loans \| Wholesale flooring \| Group I \| Performing
Current Period
Total	1,881		1,764
Prior Year
Total	1,881		1,764
Dealer loans \| Wholesale flooring \| Group II \| Performing
Current Period
Total	1,321		1,241
Prior Year
Total	1,321		1,241
Dealer loans \| Wholesale flooring \| Group III \| Performing
Current Period
Total	1		1
Prior Year
Total	$ 1		$ 1

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