Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Segment Reporting Information [Line Items]
Total financing revenues	$ 2,890	$ 2,647	$ 5,726	$ 5,245
Depreciation on operating leases	1,662	1,719	3,428	3,400
Interest expense	702	452	1,384	900
Net financing revenues	526	476	914	945
Insurance earned premiums and contract revenues	226	221	450	437
Investment and other income, net	56	56	96	144
Net financing revenues and other revenues	808	753	1,460	1,526
Expenses:
Provision for credit losses	67	127	156	212
Operating and administrative expenses	348	337	672	650
Insurance losses and loss adjustment expenses	112	102	237	216
Total expenses	527	566	1,065	1,078
Income before income taxes	281	187	395	448
Provision for income taxes	87	70	109	166
Net income	194	117	286	282
Total assets	121,060	120,100	121,060	120,100	$ 120,546
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	(5)	(3)	(10)	(6)
Net financing revenues	5	3	10	6
Insurance earned premiums and contract revenues	0	0	0	0
Investment and other income, net	(5)	(3)	(10)	(6)
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	(1,160)	(1,104)	(1,160)	(1,104)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	2,890	2,647	5,726	5,245
Depreciation on operating leases	1,662	1,719	3,428	3,400
Interest expense	707	455	1,394	906
Net financing revenues	521	473	904	939
Insurance earned premiums and contract revenues	0	0	0	0
Investment and other income, net	51	36	99	68
Net financing revenues and other revenues	572	509	1,003	1,007
Expenses:
Provision for credit losses	67	127	156	212
Operating and administrative expenses	262	259	503	492
Insurance losses and loss adjustment expenses	0	0	0	0
Total expenses	329	386	659	704
Income before income taxes	243	123	344	303
Provision for income taxes	77	47	96	112
Net income	166	76	248	191
Total assets	117,265	116,463	117,265	116,463
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	226	221	450	437
Investment and other income, net	10	23	7	82
Net financing revenues and other revenues	236	244	457	519
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative expenses	86	78	169	158
Insurance losses and loss adjustment expenses	112	102	237	216
Total expenses	198	180	406	374
Income before income taxes	38	64	51	145
Provision for income taxes	10	23	13	54
Net income	28	41	38	91
Total assets	$ 4,955	$ 4,741	$ 4,955	$ 4,741