Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Total financing revenues	$ 2,946	$ 2,968	$ 2,890	$ 2,836	$ 2,766	$ 2,706	$ 2,647	$ 2,598	$ 11,640	$ 10,717	$ 10,046
Depreciation on operating leases	1,764	1,717	1,662	1,766	1,863	1,778	1,719	1,681	6,909	7,041	6,853
Interest expense	664	699	702	682	523	428	452	448	2,747	1,851	1,754
Net financing revenues	518	552	526	388	380	500	476	469	1,984	1,825	1,439
Insurance earned premiums and contract revenues	228	226	226	224	225	220	221	216	904	882	804
Investment and other income, net	128	68	56	40	47	66	56	88	292	257	396
Net financing revenues and other revenues	874	846	808	652	652	786	753	773	3,180	2,964	2,639
Expenses:
Provision for credit losses	106	110	67	89	81	108	127	85	372	401	582
Operating and administrative expenses	366	347	348	324	384	323	337	313	1,385	1,357	1,277
Insurance losses and loss adjustment expenses	103	106	112	125	109	100	102	114	446	425	371
Total expenses	575	563	527	538	574	531	566	512	2,203	2,183	2,230
Income before income taxes	299	283	281	114	78	255	187	261	977	781	409
Provision (benefit) for income taxes	4	69	87	22	26	(2,821)	70	96	182	(2,629)	142
Net income	295	$ 214	$ 194	$ 92	52	$ 3,076	$ 117	$ 165	795	3,410	267
Total assets	116,516				120,546				116,516	120,546	119,635
Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Total financing revenues									0	0	0
Depreciation on operating leases									0	0	0
Interest expense									(22)	(12)	(5)
Net financing revenues									22	12	5
Insurance earned premiums and contract revenues									0	0	0
Investment and other income, net									(22)	(12)	(5)
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	(1,165)				(1,087)				(1,165)	(1,087)	(1,083)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues									11,640	10,717	10,046
Depreciation on operating leases									6,909	7,041	6,853
Interest expense									2,769	1,863	1,759
Net financing revenues									1,962	1,813	1,434
Insurance earned premiums and contract revenues									0	0	0
Investment and other income, net									188	140	337
Net financing revenues and other revenues									2,150	1,953	1,771
Expenses:
Provision for credit losses									372	401	582
Operating and administrative expenses									1,038	1,028	979
Insurance losses and loss adjustment expenses									0	0	0
Total expenses									1,410	1,429	1,561
Income before income taxes									740	524	210
Provision (benefit) for income taxes									147	(2,654)	67
Net income									593	3,178	143
Total assets	112,615				116,942				112,615	116,942	116,242
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									904	882	804
Investment and other income, net									126	129	64
Net financing revenues and other revenues									1,030	1,011	868
Expenses:
Provision for credit losses									0	0	0
Operating and administrative expenses									347	329	298
Insurance losses and loss adjustment expenses									446	425	371
Total expenses									793	754	669
Income before income taxes									237	257	199
Provision (benefit) for income taxes									35	25	75
Net income									202	232	124
Total assets	$ 5,066				$ 4,691				$ 5,066	$ 4,691	$ 4,476