Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2012
Segment Reporting Information [Line Items]
Total financing revenues	$ 1,815	$ 1,835	$ 5,423	$ 5,625
Insurance earned premiums and contract revenues	140	150	435	453
Investment and other income	63	62	136	93
Total gross revenues	2,018	2,047	5,994	6,171
Depreciation on operating leases	901	844	2,636	2,498
Interest expense	284	163	625	769
Provision for credit losses	88	56	107	(136)
Operating and administrative expenses	229	208	674	617
Insurance losses and loss adjustment expenses	77	78	231	247
Provision for income taxes	156	266	635	828
Net income	283	432	1,086	1,348
Total assets	93,175	91,514	93,175	91,514	88,913
Finance Operations [Member]
Segment Reporting Information [Line Items]
Total financing revenues	1,809	1,831	5,405	5,614
Insurance earned premiums and contract revenues	0	0	0	0
Investment and other income	12	12	33	34
Total gross revenues	1,821	1,843	5,438	5,648
Depreciation on operating leases	901	844	2,636	2,498
Interest expense	284	163	625	772
Provision for credit losses	88	56	107	(136)
Operating and administrative expenses	182	170	542	503
Insurance losses and loss adjustment expenses	0	0	0	0
Provision for income taxes	126	232	560	768
Net income	240	378	968	1,243
Total assets	90,184	88,688	90,184	88,688
Insurance Operations [Member]
Segment Reporting Information [Line Items]
Total financing revenues	0	0	0	0
Insurance earned premiums and contract revenues	146	154	453	464
Investment and other income	51	50	103	62
Total gross revenues	197	204	556	526
Depreciation on operating leases	0	0	0	0
Interest expense	0	0	0	0
Provision for credit losses	0	0	0	0
Operating and administrative expenses	47	38	132	114
Insurance losses and loss adjustment expenses	77	78	231	247
Provision for income taxes	30	34	75	60
Net income	43	54	118	105
Total assets	3,454	3,201	3,454	3,201
Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Total financing revenues	6	4	18	11
Insurance earned premiums and contract revenues	(6)	(4)	(18)	(11)
Investment and other income	0	0	0	(3)
Total gross revenues	0	0	0	(3)
Depreciation on operating leases	0	0	0	0
Interest expense	0	0	0	(3)
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
Provision for income taxes	0	0	0	0
Net income	0	0	0	0
Total assets	$ (463)	$ (375)	$ (463)	$ (375)