Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Segment Reporting Information [Line Items]
Total financing revenues	$ 2,706	$ 2,537	$ 7,951	$ 7,491
Depreciation on operating leases	1,778	1,722	5,178	4,994
Interest expense	428	701	1,328	1,305
Net financing revenues	500	114	1,445	1,192
Insurance earned premiums and contract revenues	220	202	657	594
Investment and other income, net	63	52	165	133
Realized gains (losses), net on investments in marketable securities	3	157	45	240
Net financing revenues and other revenues	786	525	2,312	2,159
Expenses:
Provision for credit losses	108	183	320	396
Operating and administrative expenses	323	325	973	921
Insurance losses and loss adjustment expenses	100	92	316	272
Total expenses	531	600	1,609	1,589
Income (loss) before income taxes	255	(75)	703	570
(Benefit) provision for income taxes	(2,821)	(29)	(2,655)	212
Net income (loss)	3,076	(46)	3,358	358
Total assets	120,734	117,641	120,734	117,641	$ 119,635
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	(3)	0	(9)	0
Net financing revenues	3	0	9	0
Insurance earned premiums and contract revenues	0	0	0	0
Investment and other income, net	(3)	0	(9)	0
Realized gains (losses), net on investments in marketable securities	0	0	0	0
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 (loss) before income taxes	0	0	0	0
(Benefit) provision for income taxes	0	0	0	0
Net income (loss)	0	0	0	0
Total assets	(1,116)	(1,072)	(1,116)	(1,072)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	2,706	2,537	7,951	7,491
Depreciation on operating leases	1,778	1,722	5,178	4,994
Interest expense	431	701	1,337	1,305
Net financing revenues	497	114	1,436	1,192
Insurance earned premiums and contract revenues	0	0	0	0
Investment and other income, net	37	20	105	68
Realized gains (losses), net on investments in marketable securities	0	155	0	241
Net financing revenues and other revenues	534	289	1,541	1,501
Expenses:
Provision for credit losses	108	183	320	396
Operating and administrative expenses	239	250	731	702
Insurance losses and loss adjustment expenses	0	0	0	0
Total expenses	347	433	1,051	1,098
Income (loss) before income taxes	187	(144)	490	403
(Benefit) provision for income taxes	(2,780)	(55)	(2,668)	150
Net income (loss)	2,967	(89)	3,158	253
Total assets	117,147	114,292	117,147	114,292
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	220	202	657	594
Investment and other income, net	29	32	69	65
Realized gains (losses), net on investments in marketable securities	3	2	45	(1)
Net financing revenues and other revenues	252	236	771	658
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative expenses	84	75	242	219
Insurance losses and loss adjustment expenses	100	92	316	272
Total expenses	184	167	558	491
Income (loss) before income taxes	68	69	213	167
(Benefit) provision for income taxes	(41)	26	13	62
Net income (loss)	109	43	200	105
Total assets	$ 4,703	$ 4,421	$ 4,703	$ 4,421