Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2020
Segment Reporting Information [Line Items]
Total financing revenues	$ 2,935	$ 3,018	$ 5,847	$ 5,981
Depreciation on operating leases	1,349	1,583	3,034	3,208
Interest expense	495	613	1,043	1,310
Net financing revenues	1,091	822	1,770	1,463
Insurance earned premiums and contract revenues	238	232	473	461
Investment and other income, net	90	97	266	215
Net financing revenues and other revenues	1,419	1,151	2,509	2,139
Expenses:
Provision for credit losses	65	61	248	136
Operating and administrative expenses	389	358	734	695
Insurance losses and loss adjustment expenses	92	115	167	228
Total expenses	546	534	1,149	1,059
Income before income taxes	873	617	1,360	1,080
Provision for income taxes	218	158	331	262
Net income	655	459	1,029	818
Total assets	131,067	119,938	131,067	119,938	$ 125,555
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	(6)	0	(12)
Net financing revenues	0	6	0	12
Insurance earned premiums and contract revenues	0	0	0	0
Investment and other income, net	0	(6)	0	(12)
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
Insurance losses and loss adjustment expenses	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	(135)	(1,190)	(135)	(1,190)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	2,935	3,018	5,847	5,981
Depreciation on operating leases	1,349	1,583	3,034	3,208
Interest expense	495	619	1,043	1,322
Net financing revenues	1,091	816	1,770	1,451
Insurance earned premiums and contract revenues	0	0	0	0
Investment and other income, net	23	38	55	75
Net financing revenues and other revenues	1,114	854	1,825	1,526
Expenses:
Provision for credit losses	65	61	248	136
Operating and administrative expenses	294	268	550	514
Insurance losses and loss adjustment expenses	0	0	0	0
Total expenses	359	329	798	650
Income before income taxes	755	525	1,027	876
Provision for income taxes	189	136	251	212
Net income	566	389	776	664
Total assets	125,277	115,714	125,277	115,714
Insurance 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
Insurance earned premiums and contract revenues	238	232	473	461
Investment and other income, net	67	65	211	152
Net financing revenues and other revenues	305	297	684	613
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative expenses	95	90	184	181
Insurance losses and loss adjustment expenses	92	115	167	228
Total expenses	187	205	351	409
Income before income taxes	118	92	333	204
Provision for income taxes	29	22	80	50
Net income	89	70	253	154
Total assets	$ 5,925	$ 5,414	$ 5,925	$ 5,414