Finance Receivables, Net - Schedule of Amortized Cost Basis of Retail Loan Portfolio and Dealer Products Portfolio by Credit Quality Indicator (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2024	Mar. 31, 2024
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	$ 1,190	$ 1,190	$ 2,083
Year two, originated, fiscal year before current fiscal year	1,788	1,788	1,381
Year three, originated, two years before current fiscal year	1,086	1,086	1,117
Year four, originated, three years before current fiscal year	911	911	1,026
Year five, originated, four years before current fiscal year	927	927	235
Originated, more than five years before current fiscal year	968	968	945
Revolving loans	9,510	9,510	9,394
Total	16,380	16,380	16,181
Gross Charge-Offs, Total	0	0	0
Retail Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	18,331	18,331	35,823
Year two, originated, fiscal year before current fiscal year	30,368	30,368	23,173
Year three, originated, two years before current fiscal year	18,897	18,897	15,639
Year four, originated, three years before current fiscal year	12,417	12,417	8,878
Year five, originated, four years before current fiscal year	6,462	6,462	2,783
Originated, more than five years before current fiscal year	2,038	2,038	829
Total	88,513	88,513	87,125
Gross Charge-Offs, year one, originated, current fiscal year		1	38
Gross Charge-Offs, Year two, originated, fiscal year before current fiscal year		105	297
Gross Charge-Offs, Year three, originated, two years before current fiscal year		161	258
Gross Charge-Offs, Year four, originated, three years before current fiscal year		104	111
Gross Charge-Offs, Year five, originated, four years before current fiscal year		41	38
Gross Charge-Offs, Originated, more than five years before current fiscal year		23	34
Gross Charge-Offs, Total		435	776
Current [Member] | Retail Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	18,204	18,204	35,407
Year two, originated, fiscal year before current fiscal year	29,732	29,732	22,473
Year three, originated, two years before current fiscal year	18,148	18,148	15,041
Year four, originated, three years before current fiscal year	11,827	11,827	8,539
Year five, originated, four years before current fiscal year	6,140	6,140	2,654
Originated, more than five years before current fiscal year	1,881	1,881	748
Total	85,932	85,932	84,862
30-59 Days Past Due [Member] | Retail Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	92	92	301
Year two, originated, fiscal year before current fiscal year	428	428	488
Year three, originated, two years before current fiscal year	506	506	426
Year four, originated, three years before current fiscal year	409	409	242
Year five, originated, four years before current fiscal year	225	225	92
Originated, more than five years before current fiscal year	102	102	53
Total	1,762	1,762	1,602
60-89 Days Past Due [Member] | Retail Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	26	26	77
Year two, originated, fiscal year before current fiscal year	138	138	143
Year three, originated, two years before current fiscal year	162	162	119
Year four, originated, three years before current fiscal year	125	125	68
Year five, originated, four years before current fiscal year	68	68	27
Originated, more than five years before current fiscal year	35	35	17
Total	554	554	451
90 Days or Greater Past Due [Member] | Retail Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	9	9	38
Year two, originated, fiscal year before current fiscal year	70	70	69
Year three, originated, two years before current fiscal year	81	81	53
Year four, originated, three years before current fiscal year	56	56	29
Year five, originated, four years before current fiscal year	29	29	10
Originated, more than five years before current fiscal year	20	20	11
Total	265	265	210
Wholesale [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	0	0	0
Year two, originated, fiscal year before current fiscal year	0	0	0
Year three, originated, two years before current fiscal year	0	0	0
Year four, originated, three years before current fiscal year	0	0	0
Year five, originated, four years before current fiscal year	0	0	0
Originated, more than five years before current fiscal year	0	0	0
Revolving loans	6,360	6,360	6,673
Total	6,360	6,360	6,673
Wholesale [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	0	0	0
Year two, originated, fiscal year before current fiscal year	0	0	0
Year three, originated, two years before current fiscal year	0	0	0
Year four, originated, three years before current fiscal year	0	0	0
Year five, originated, four years before current fiscal year	0	0	0
Originated, more than five years before current fiscal year	0	0	0
Revolving loans	5,952	5,952	6,287
Total	5,952	5,952	6,287
Wholesale [Member] | Credit Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	0	0	0
Year two, originated, fiscal year before current fiscal year	0	0	0
Year three, originated, two years before current fiscal year	0	0	0
Year four, originated, three years before current fiscal year	0	0	0
Year five, originated, four years before current fiscal year	0	0	0
Originated, more than five years before current fiscal year	0	0	0
Revolving loans	379	379	238
Total	379	379	238
Wholesale [Member] | At Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	0	0	0
Year two, originated, fiscal year before current fiscal year	0	0	0
Year three, originated, two years before current fiscal year	0	0	0
Year four, originated, three years before current fiscal year	0	0	0
Year five, originated, four years before current fiscal year	0	0	0
Originated, more than five years before current fiscal year	0	0	0
Revolving loans	21	21	112
Total	21	21	112
Wholesale [Member] | Default [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	0	0	0
Year two, originated, fiscal year before current fiscal year	0	0	0
Year three, originated, two years before current fiscal year	0	0	0
Year four, originated, three years before current fiscal year	0	0	0
Year five, originated, four years before current fiscal year	0	0	0
Originated, more than five years before current fiscal year	0	0	0
Revolving loans	8	8	36
Total	8	8	36
Real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	788	788	1,294
Year two, originated, fiscal year before current fiscal year	1,149	1,149	923
Year three, originated, two years before current fiscal year	783	783	869
Year four, originated, three years before current fiscal year	729	729	891
Year five, originated, four years before current fiscal year	815	815	128
Originated, more than five years before current fiscal year	737	737	786
Revolving loans	208	208	3
Total	5,209	5,209	4,894
Real estate [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	713	713	1,224
Year two, originated, fiscal year before current fiscal year	1,094	1,094	883
Year three, originated, two years before current fiscal year	783	783	815
Year four, originated, three years before current fiscal year	701	701	860
Year five, originated, four years before current fiscal year	800	800	128
Originated, more than five years before current fiscal year	735	735	784
Revolving loans	208	208	3
Total	5,034	5,034	4,697
Real estate [Member] | Credit Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	70	70	58
Year two, originated, fiscal year before current fiscal year	46	46	37
Year three, originated, two years before current fiscal year	0	0	44
Year four, originated, three years before current fiscal year	28	28	6
Year five, originated, four years before current fiscal year	15	15	0
Originated, more than five years before current fiscal year	0	0	0
Revolving loans	0	0	0
Total	159	159	145
Real estate [Member] | At Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	0	0	8
Year two, originated, fiscal year before current fiscal year	9	9	1
Year three, originated, two years before current fiscal year	0	0	10
Year four, originated, three years before current fiscal year	0	0	0
Year five, originated, four years before current fiscal year	0	0	0
Originated, more than five years before current fiscal year	2	2	2
Revolving loans	0	0	0
Total	11	11	21
Real estate [Member] | Default [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	5	5	4
Year two, originated, fiscal year before current fiscal year	0	0	2
Year three, originated, two years before current fiscal year	0	0	0
Year four, originated, three years before current fiscal year	0	0	25
Year five, originated, four years before current fiscal year	0	0	0
Originated, more than five years before current fiscal year	0	0	0
Revolving loans	0	0	0
Total	5	5	31
Working capital [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	402	402	789
Year two, originated, fiscal year before current fiscal year	639	639	458
Year three, originated, two years before current fiscal year	303	303	248
Year four, originated, three years before current fiscal year	182	182	135
Year five, originated, four years before current fiscal year	112	112	107
Originated, more than five years before current fiscal year	231	231	159
Revolving loans	2,942	2,942	2,718
Total	4,811	4,811	4,614
Working capital [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	391	391	769
Year two, originated, fiscal year before current fiscal year	627	627	414
Year three, originated, two years before current fiscal year	286	286	235
Year four, originated, three years before current fiscal year	178	178	122
Year five, originated, four years before current fiscal year	112	112	105
Originated, more than five years before current fiscal year	231	231	159
Revolving loans	2,939	2,939	2,715
Total	4,764	4,764	4,519
Working capital [Member] | Credit Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	11	11	20
Year two, originated, fiscal year before current fiscal year	12	12	41
Year three, originated, two years before current fiscal year	14	14	13
Year four, originated, three years before current fiscal year	4	4	0
Year five, originated, four years before current fiscal year	0	0	0
Originated, more than five years before current fiscal year	0	0	0
Revolving loans	2	2	2
Total	43	43	76
Working capital [Member] | At Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	0	0	0
Year two, originated, fiscal year before current fiscal year	0	0	3
Year three, originated, two years before current fiscal year	3	3	0
Year four, originated, three years before current fiscal year	0	0	0
Year five, originated, four years before current fiscal year	0	0	2
Originated, more than five years before current fiscal year	0	0	0
Revolving loans	1	1	1
Total	4	4	6
Working capital [Member] | Default [Member]
Financing Receivable, Recorded Investment [Line Items]
Year one, originated, current fiscal year	0	0	0
Year two, originated, fiscal year before current fiscal year	0	0	0
Year three, originated, two years before current fiscal year	0	0	0
Year four, originated, three years before current fiscal year	0	0	13
Year five, originated, four years before current fiscal year	0	0	0
Originated, more than five years before current fiscal year	0	0	0
Revolving loans	0	0	0
Total	$ 0	$ 0	$ 13