Selected Quarterly Financial Data - Selected Quarterly Financial Data (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
Financing revenues:
Operating lease	$ 2,182	$ 2,212	$ 2,197	$ 2,184	$ 2,189	$ 2,212	$ 2,167	$ 2,126	$ 8,775	$ 8,694	$ 8,167
Retail	670	661	638	589	575	578	547	535	2,558	2,235	1,974
Dealer	152	171	183	190	182	178	176	175	696	711	576
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	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