Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Mar. 31, 2023
Segment Reporting Information [Line Items]
Total financing revenues	$ 3,098	$ 2,856	$ 8,988	$ 8,511
Depreciation on operating leases	1,063	1,262	3,145	3,976
Interest expense	1,230	765	3,401	2,033
Net financing revenues	805	829	2,442	2,502
Voluntary protection contract revenues and insurance earned premiums	282	263	831	785
Investment and other income (loss), net	495	240	639	(204)
Net financing revenues and other revenues	1,582	1,332	3,912	3,083
Expenses:
Provision for credit losses	206	278	592	569
Operating and administrative	517	463	1,414	1,313
Voluntary protection contract expenses and insurance losses	143	115	434	336
Total expenses	866	856	2,440	2,218
Income (loss) before income taxes	716	476	1,472	865
Provision (benefit) for income taxes	113	112	154	212
Net income (loss)	603	364	1,318	653
Total assets	146,818	137,630	146,818	137,630	$ 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	(58)	(124)	(58)	(124)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	3,098	2,856	8,988	8,511
Depreciation on operating leases	1,063	1,262	3,145	3,976
Interest expense	1,230	765	3,401	2,033
Net financing revenues	805	829	2,442	2,502
Voluntary protection contract revenues and insurance earned premiums	0	0	0	0
Investment and other income (loss), net	142	97	375	185
Net financing revenues and other revenues	947	926	2,817	2,687
Expenses:
Provision for credit losses	206	278	592	569
Operating and administrative	407	345	1,073	983
Voluntary protection contract expenses and insurance losses	0	0	0	0
Total expenses	613	623	1,665	1,552
Income (loss) before income taxes	334	303	1,152	1,135
Provision (benefit) for income taxes	33	70	81	281
Net income (loss)	301	233	1,071	854
Total assets	139,575	131,402	139,575	131,402
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	282	263	831	785
Investment and other income (loss), net	353	143	264	(389)
Net financing revenues and other revenues	635	406	1,095	396
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative	110	118	341	330
Voluntary protection contract expenses and insurance losses	143	115	434	336
Total expenses	253	233	775	666
Income (loss) before income taxes	382	173	320	(270)
Provision (benefit) for income taxes	80	42	73	(69)
Net income (loss)	302	131	247	(201)
Total assets	$ 7,301	$ 6,352	$ 7,301	$ 6,352