Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Mar. 31, 2024
Segment Reporting Information [Line Items]
Total financing revenues	$ 3,297	$ 2,986	$ 6,506	$ 5,890
Depreciation on operating leases	1,015	918	2,049	2,073
Interest expense	1,584	1,272	3,027	2,171
Net financing revenues	698	796	1,430	1,646
Voluntary protection contract revenues and insurance earned premiums	300	278	595	549
Investment and other income (loss), net	388	(18)	611	144
Net financing revenues and other revenues	1,386	1,056	2,636	2,339
Expenses:
Provision for credit losses	206	221	395	386
Operating and administrative	453	449	893	897
Voluntary protection contract expenses and insurance losses	161	145	320	291
Total expenses	820	815	1,608	1,574
Income before income taxes	566	241	1,028	765
Provision (benefit) for income taxes	137	63	242	195
Net Income (Loss)	429	178	786	570
Total assets	153,551	139,715	153,551	139,715	$ 149,381
Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Total financing revenues	0	0	0	0
Depreciation on operating leases	0	0	0	0
Interest expense	0	0	0	0
Net financing revenues	0	0	0	0
Voluntary protection contract revenues and insurance earned premiums	0	0	0	0
Investment and other income (loss), net	0	0	0	0
Net financing revenues and other revenues	0	0	0	0
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative	0	0	0	0
Voluntary protection contract expenses and insurance losses	0	0	0	0
Total expenses	0	0	0	0
Income before income taxes	0	0	0	0
Provision (benefit) for income taxes	0	0	0	0
Net Income (Loss)	0	0	0	0
Total assets	(93)	(78)	(93)	(78)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	3,297	2,986	6,506	5,890
Depreciation on operating leases	1,015	918	2,049	2,073
Interest expense	1,584	1,272	3,027	2,171
Net financing revenues	698	796	1,430	1,646
Voluntary protection contract revenues and insurance earned premiums	0	0	0	0
Investment and other income (loss), net	136	119	302	233
Net financing revenues and other revenues	834	915	1,732	1,879
Expenses:
Provision for credit losses	206	221	395	386
Operating and administrative	332	332	659	666
Voluntary protection contract expenses and insurance losses		0	0	0
Total expenses	538	553	1,054	1,052
Income before income taxes	296	362	678	827
Provision (benefit) for income taxes	74	83	161	202
Net Income (Loss)	222	279	517	625
Total assets	145,636	133,013	145,636	133,013
Voluntary Protection Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	0	0	0	0
Depreciation on operating leases	0	0	0	0
Interest expense	0	0	0	0
Net financing revenues	0	0	0	0
Voluntary protection contract revenues and insurance earned premiums	300	278	595	549
Investment and other income (loss), net	252	(137)	309	(89)
Net financing revenues and other revenues	552	141	904	460
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative	121	117	234	231
Voluntary protection contract expenses and insurance losses	161	145	320	291
Total expenses	282	262	554	522
Income before income taxes	270	(121)	350	(62)
Provision (benefit) for income taxes	63	(20)	81	(7)
Net Income (Loss)	207	(101)	269	(55)
Total assets	$ 8,008	$ 6,780	$ 8,008	$ 6,780