Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Mar. 31, 2021
Segment Reporting Information [Line Items]
Total financing revenues	$ 3,032	$ 2,935	$ 6,031	$ 5,847
Depreciation on operating leases	1,499	1,349	2,940	3,034
Interest expense	423	495	709	1,043
Net financing revenues	1,110	1,091	2,382	1,770
Voluntary protection contract revenues and insurance earned premiums	254	238	503	473
Investment and other income (loss), net	7	90	163	266
Net financing revenues and other revenues	1,371	1,419	3,048	2,509
Expenses:
Provision for credit losses	68	65	65	248
Operating and administrative expenses	385	389	769	734
Voluntary protection contract expenses and insurance losses	99	92	207	167
Total expenses	552	546	1,041	1,149
Income before income taxes	819	873	2,007	1,360
Provision for income taxes	197	218	464	331
Net income	622	655	1,543	1,029
Total assets	136,977	131,067	136,977	131,067	$ 133,728
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 expenses	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 for income taxes	0	0	0	0
Net income	0	0	0	0
Total assets	(138)	(135)	(138)	(135)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	3,032	2,935	6,031	5,847
Depreciation on operating leases	1,499	1,349	2,940	3,034
Interest expense	423	495	709	1,043
Net financing revenues	1,110	1,091	2,382	1,770
Voluntary protection contract revenues and insurance earned premiums	0	0	0	0
Investment and other income (loss), net	9	23	28	55
Net financing revenues and other revenues	1,119	1,114	2,410	1,825
Expenses:
Provision for credit losses	68	65	65	248
Operating and administrative expenses	287	294	579	550
Voluntary protection contract expenses and insurance losses	0	0	0	0
Total expenses	355	359	644	798
Income before income taxes	764	755	1,766	1,027
Provision for income taxes	185	189	406	251
Net income	579	566	1,360	776
Total assets	130,544	125,277	130,544	125,277
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	254	238	503	473
Investment and other income (loss), net	(2)	67	135	211
Net financing revenues and other revenues	252	305	638	684
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative expenses	98	95	190	184
Voluntary protection contract expenses and insurance losses	99	92	207	167
Total expenses	197	187	397	351
Income before income taxes	55	118	241	333
Provision for income taxes	12	29	58	80
Net income	43	89	183	253
Total assets	$ 6,571	$ 5,925	$ 6,571	$ 5,925