Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2020
Segment Reporting Information [Line Items]
Total financing revenues	$ 2,974	$ 3,044	$ 8,821	$ 9,025
Depreciation on operating leases	1,450	1,712	4,484	4,920
Interest expense	491	755	1,534	2,065
Net financing revenues	1,033	577	2,803	2,040
Insurance earned premiums and contract revenues	241	231	714	692
Investment and other income, net	179	57	445	272
Net financing revenues and other revenues	1,453	865	3,962	3,004
Expenses:
Provision for credit losses	118	128	366	264
Operating and administrative expenses	354	406	1,088	1,101
Insurance losses and loss adjustment expenses	98	116	265	344
Total expenses	570	650	1,719	1,709
Income before income taxes	883	215	2,243	1,295
Provision for income taxes	215	34	546	296
Net income	668	181	1,697	999
Total assets	134,491	122,607	134,491	122,607	$ 125,555
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	0	(4)	0	(16)
Net financing revenues	0	4	0	16
Insurance earned premiums and contract revenues	0	0	0	0
Investment and other income, net	0	(4)	0	(16)
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	(127)	(1,112)	(127)	(1,112)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	2,974	3,044	8,821	9,025
Depreciation on operating leases	1,450	1,712	4,484	4,920
Interest expense	491	759	1,534	2,081
Net financing revenues	1,033	573	2,803	2,024
Insurance earned premiums and contract revenues	0	0	0	0
Investment and other income, net	21	42	76	117
Net financing revenues and other revenues	1,054	615	2,879	2,141
Expenses:
Provision for credit losses	118	128	366	264
Operating and administrative expenses	268	318	818	832
Insurance losses and loss adjustment expenses	0	0	0	0
Total expenses	386	446	1,184	1,096
Income before income taxes	668	169	1,695	1,045
Provision for income taxes	163	23	414	235
Net income	505	146	1,281	810
Total assets	128,442	118,228	128,442	118,228
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	241	231	714	692
Investment and other income, net	158	19	369	171
Net financing revenues and other revenues	399	250	1,083	863
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative expenses	86	88	270	269
Insurance losses and loss adjustment expenses	98	116	265	344
Total expenses	184	204	535	613
Income before income taxes	215	46	548	250
Provision for income taxes	52	11	132	61
Net income	163	35	416	189
Total assets	$ 6,176	$ 5,491	$ 6,176	$ 5,491