Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Total financing revenues	$ 3,004	$ 3,044	$ 3,018	$ 2,963	$ 2,946	$ 2,968	$ 2,890	$ 2,836	$ 12,029	$ 11,640	$ 10,717
Depreciation on operating leases	1,900	1,712	1,583	1,625	1,764	1,717	1,662	1,766	6,820	6,909	7,041
Interest expense	769	755	613	697	664	699	702	682	2,834	2,747	1,851
Net financing revenues	335	577	822	641	518	552	526	388	2,375	1,984	1,825
Insurance earned premiums and contract revenues	241	231	232	229	228	226	226	224	933	904	882
Investment and other income, net	50	57	97	118	128	68	56	40	322	292	257
Net financing revenues and other revenues	626	865	1,151	988	874	846	808	652	3,630	3,180	2,964
Expenses:
Provision for credit losses	326	128	61	75	106	110	67	89	590	372	401
Operating and administrative expenses	460	406	358	337	366	347	348	324	1,561	1,385	1,357
Insurance losses and loss adjustment expenses	111	116	115	113	103	106	112	125	455	446	425
Total expenses	897	650	534	525	575	563	527	538	2,606	2,203	2,183
Income before income taxes	(271)	215	617	463	299	283	281	114	1,024	977	781
Provision (benefit) for income taxes	(185)	34	158	104	4	69	87	22	111	182	(2,629)
Net income	(86)	$ 181	$ 459	$ 359	295	$ 214	$ 194	$ 92	913	795	3,410
Total assets	125,555				116,516				125,555	116,516	120,546
Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Total financing revenues									0	0	0
Depreciation on operating leases									0	0	0
Interest expense									(20)	(22)	(12)
Net financing revenues									20	22	12
Insurance earned premiums and contract revenues									0	0	0
Investment and other income, net									(20)	(22)	(12)
Net financing revenues and other revenues									0	0	0
Expenses:
Provision for credit losses									0	0	0
Operating and administrative expenses									0	0	0
Insurance losses and loss adjustment expenses									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	(1,145)				(1,165)				(1,145)	(1,165)	(1,087)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues									12,029	11,640	10,717
Depreciation on operating leases									6,820	6,909	7,041
Interest expense									2,854	2,769	1,863
Net financing revenues									2,355	1,962	1,813
Insurance earned premiums and contract revenues									0	0	0
Investment and other income, net									155	188	140
Net financing revenues and other revenues									2,510	2,150	1,953
Expenses:
Provision for credit losses									590	372	401
Operating and administrative expenses									1,197	1,038	1,028
Insurance losses and loss adjustment expenses									0	0	0
Total expenses									1,787	1,410	1,429
Income before income taxes									723	740	524
Provision (benefit) for income taxes									39	147	(2,654)
Net income									684	593	3,178
Total assets	121,180				112,615				121,180	112,615	116,942
Insurance 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
Insurance earned premiums and contract revenues									933	904	882
Investment and other income, net									187	126	129
Net financing revenues and other revenues									1,120	1,030	1,011
Expenses:
Provision for credit losses									0	0	0
Operating and administrative expenses									364	347	329
Insurance losses and loss adjustment expenses									455	446	425
Total expenses									819	793	754
Income before income taxes									301	237	257
Provision (benefit) for income taxes									72	35	25
Net income									229	202	232
Total assets	$ 5,520				$ 5,066				$ 5,520	$ 5,066	$ 4,691