Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2012
Segment Reporting Information [Line Items]
Total financing revenues	$ 1,811	$ 1,870	$ 3,608	$ 3,790
Insurance earned premiums and contract revenues	145	153	295	303
Investment and other income	38	(9)	73	31
Total gross revenues	1,994	2,014	3,976	4,124
Depreciation on operating leases	880	829	1,735	1,654
Interest expense	283	149	341	606
Provision for credit losses	3	11	19	(192)
Operating and administrative expenses	229	212	445	409
Insurance losses and loss adjustment expenses	73	83	154	169
Provision for income taxes	200	279	479	562
Net income	326	451	803	916
Total assets	93,128	88,672	93,128	88,672	88,913
Finance Operations [Member]
Segment Reporting Information [Line Items]
Total financing revenues	1,805	1,867	3,596	3,783
Insurance earned premiums and contract revenues	0	0	0	0
Investment and other income	11	10	21	22
Total gross revenues	1,816	1,877	3,617	3,805
Depreciation on operating leases	880	829	1,735	1,654
Interest expense	283	150	341	609
Provision for credit losses	3	11	19	(192)
Operating and administrative expenses	187	175	360	333
Insurance losses and loss adjustment expenses	0	0	0	0
Provision for income taxes	177	274	434	536
Net income	286	438	728	865
Total assets	90,230	85,998	90,230	85,998
Insurance Operations [Member]
Segment Reporting Information [Line Items]
Total financing revenues	0	0	0	0
Insurance earned premiums and contract revenues	151	156	307	310
Investment and other income	27	(18)	52	12
Total gross revenues	178	138	359	322
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	42	37	85	76
Insurance losses and loss adjustment expenses	73	83	154	169
Provision for income taxes	23	5	45	26
Net income	40	13	75	51
Total assets	3,453	3,165	3,453	3,165
Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Total financing revenues	6	3	12	7
Insurance earned premiums and contract revenues	(6)	(3)	(12)	(7)
Investment and other income	0	(1)	0	(3)
Total gross revenues	0	(1)	0	(3)
Depreciation on operating leases	0	0	0	0
Interest expense	0	(1)	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	$ (555)	$ (491)	$ (555)	$ (491)