Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Total financing revenues	$ 2,978	$ 2,974	$ 2,935	$ 2,912	$ 3,004	$ 3,044	$ 3,018	$ 2,963	$ 11,799	$ 12,029	$ 11,640
Depreciation on operating leases	1,448	1,450	1,349	1,685	1,900	1,712	1,583	1,625	5,932	6,820	6,909
Interest expense	768	491	495	548	769	755	613	697	2,302	2,834	2,747
Net financing revenues	762	1,033	1,091	679	335	577	822	641	3,565	2,375	1,984
Voluntary protection contract revenues and insurance earned premiums	242	241	238	235	241	231	232	229	956	933	904
Investment and other income, net	(35)	179	90	176	50	57	97	118	410	322	292
Net financing revenues and other revenues	969	1,453	1,419	1,090	626	865	1,151	988	4,931	3,630	3,180
Expenses:
Provision for credit losses	60	118	65	183	326	128	61	75	426	590	372
Operating and administrative expenses	399	354	389	345	460	406	358	337	1,487	1,561	1,385
Voluntary protection contract expenses and insurance losses	104	98	92	75	111	116	115	113	369	455	446
Total expenses	563	570	546	603	897	650	534	525	2,282	2,606	2,203
Income before income taxes	406	883	873	487	(271)	215	617	463	2,649	1,024	977
Provision for income taxes	86	215	218	113	(185)	34	158	104	632	111	182
Net income	320	$ 668	$ 655	$ 374	(86)	$ 181	$ 459	$ 359	2,017	913	795
Total assets	133,728				125,555				133,728	125,555	116,516
Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Total financing revenues									0	0	0
Depreciation on operating leases									0	0	0
Interest expense									0	(20)	(22)
Net financing revenues									0	20	22
Voluntary protection contract revenues and insurance earned premiums									0	0	0
Investment and other income, net									0	(20)	(22)
Net financing revenues and other revenues									0	0	0
Expenses:
Provision for credit losses									0	0	0
Operating and administrative expenses									0	0	0
Voluntary protection contract expenses and insurance losses									0	0	0
Total expenses									0	0	0
Income before income taxes									0	0	0
Provision for income taxes									0	0	0
Net income									0	0	0
Total assets	(147)				(1,145)				(147)	(1,145)	(1,165)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues									11,799	12,029	11,640
Depreciation on operating leases									5,932	6,820	6,909
Interest expense									2,302	2,854	2,769
Net financing revenues									3,565	2,355	1,962
Voluntary protection contract revenues and insurance earned premiums									0	0	0
Investment and other income, net									93	155	188
Net financing revenues and other revenues									3,658	2,510	2,150
Expenses:
Provision for credit losses									426	590	372
Operating and administrative expenses									1,124	1,197	1,038
Voluntary protection contract expenses and insurance losses									0	0	0
Total expenses									1,550	1,787	1,410
Income before income taxes									2,108	723	740
Provision for income taxes									502	39	147
Net income									1,606	684	593
Total assets	127,726				121,180				127,726	121,180	112,615
Voluntary Protection 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
Voluntary protection contract revenues and insurance earned premiums									956	933	904
Investment and other income, net									317	187	126
Net financing revenues and other revenues									1,273	1,120	1,030
Expenses:
Provision for credit losses									0	0	0
Operating and administrative expenses									363	364	347
Voluntary protection contract expenses and insurance losses									369	455	446
Total expenses									732	819	793
Income before income taxes									541	301	237
Provision for income taxes									130	72	35
Net income									411	229	202
Total assets	$ 6,149				$ 5,520				$ 6,149	$ 5,520	$ 5,066