Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Mar. 31, 2023
Segment Reporting Information [Line Items]
Total financing revenues	$ 2,986	$ 2,824	$ 5,890	$ 5,655
Depreciation on operating leases	925	1,305	2,082	2,714
Interest expense	1,272	705	2,171	1,268
Net financing revenues	789	814	1,637	1,673
Voluntary protection contract revenues and insurance earned premiums	278	263	549	522
Investment and other income (loss), net	(18)	(138)	144	(444)
Net financing revenues and other revenues	1,049	939	2,330	1,751
Expenses:
Provision for credit losses	221	213	386	291
Operating and administrative	449	444	897	850
Voluntary protection contract expenses and insurance losses	145	114	291	221
Total expenses	815	771	1,574	1,362
Income (loss) before income taxes	234	168	756	389
Provision (benefit) for income taxes	(13)	49	41	100
Net income (loss)	247	119	715	289
Total assets	139,902	134,352	139,902	134,352	$ 137,595
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 (loss) 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	(78)	(128)	(78)	(128)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	2,986	2,824	5,890	5,655
Depreciation on operating leases	925	1,305	2,082	2,714
Interest expense	1,272	705	2,171	1,268
Net financing revenues	789	814	1,637	1,673
Voluntary protection contract revenues and insurance earned premiums	0	0	0	0
Investment and other income (loss), net	119	55	233	88
Net financing revenues and other revenues	908	869	1,870	1,761
Expenses:
Provision for credit losses	221	213	386	291
Operating and administrative	332	339	666	638
Voluntary protection contract expenses and insurance losses	0	0	0	0
Total expenses	553	552	1,052	929
Income (loss) before income taxes	355	317	818	832
Provision (benefit) for income taxes	7	86	48	211
Net income (loss)	348	231	770	621
Total assets	133,200	128,403	133,200	128,403
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	278	263	549	522
Investment and other income (loss), net	(137)	(193)	(89)	(532)
Net financing revenues and other revenues	141	70	460	(10)
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative	117	105	231	212
Voluntary protection contract expenses and insurance losses	145	114	291	221
Total expenses	262	219	522	433
Income (loss) before income taxes	(121)	(149)	(62)	(443)
Provision (benefit) for income taxes	(20)	(37)	(7)	(111)
Net income (loss)	(101)	(112)	(55)	(332)
Total assets	$ 6,780	$ 6,077	$ 6,780	$ 6,077