Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Total financing revenues	$ 3,156	$ 3,098	$ 2,986	$ 2,904	$ 12,144	$ 11,293	$ 11,920
Depreciation on operating leases	1,062	1,044	918	1,155	4,179	5,122	5,846
Interest expense	1,304	1,230	1,272	899	4,705	3,054	1,401
Net financing revenues	790	824	796	850	3,260	3,117	4,673
Voluntary protection contract revenues and insurance earned premiums	289	282	278	271	1,120	1,053	1,015
Investment and other income (loss), net	234	495	(18)	162	873	97	(26)
Net financing revenues and other revenues	1,313	1,601	1,056	1,283	5,253	4,267	5,662
Expenses:
Provision for credit losses					839	713	236
Operating and administrative					1,920	1,776	1,697
Voluntary protection contract expenses and insurance losses					592	470	405
Total expenses	911	866	815	759	3,351	2,959	2,338
Income before income taxes	402	735	241	524	1,902	1,308	3,324
Provision (benefit) for income taxes	73	174	63	132	442	329	789
Net income	329	$ 561	$ 178	$ 392	1,460	979	2,535
Total assets	149,381				149,381	137,595	135,041
Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Total financing revenues					0	0	0
Depreciation on operating leases					0	0	0
Interest expense					0	0	0
Net financing revenues					0	0	0
Voluntary protection contract revenues and insurance earned premiums					0	0	0
Investment and other income (loss), net					0	0	0
Net financing revenues and other revenues					0	0	0
Expenses:
Provision for credit losses					0	0	0
Operating and administrative					0	0	0
Voluntary protection contract expenses and insurance losses					0	0	0
Total expenses					0	0	0
Income before income taxes					0	0	0
Provision (benefit) for income taxes					0	0	0
Net income					0	0	0
Total assets	(78)				(78)	(136)	(153)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues					12,144	11,293	11,920
Depreciation on operating leases					4,179	5,122	5,846
Interest expense					4,705	3,054	1,401
Net financing revenues					3,260	3,117	4,673
Voluntary protection contract revenues and insurance earned premiums					0	0	0
Investment and other income (loss), net					515	314	45
Net financing revenues and other revenues					3,775	3,431	4,718
Expenses:
Provision for credit losses					839	713	236
Operating and administrative					1,466	1,331	1,311
Voluntary protection contract expenses and insurance losses					0	0	0
Total expenses					2,305	2,044	1,547
Income before income taxes					1,470	1,387	3,171
Provision (benefit) for income taxes					344	346	755
Net income					1,126	1,041	2,416
Total assets	141,993				141,993	131,093	128,684
Voluntary Protection Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues					0	0	0
Depreciation on operating leases					0	0	0
Interest expense					0	0	0
Net financing revenues					0	0	0
Voluntary protection contract revenues and insurance earned premiums					1,120	1,053	1,015
Investment and other income (loss), net					358	(217)	(71)
Net financing revenues and other revenues					1,478	836	944
Expenses:
Provision for credit losses					0	0	0
Operating and administrative					454	445	386
Voluntary protection contract expenses and insurance losses					592	470	405
Total expenses					1,046	915	791
Income before income taxes					432	(79)	153
Provision (benefit) for income taxes					98	(17)	34
Net income					334	(62)	119
Total assets	$ 7,466				$ 7,466	$ 6,638	$ 6,510