Selected Quarterly Financial Data (Unaudited) - Selected Quarterly Financial Data (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Total financing revenues	$ 2,181	$ 2,112	$ 2,057	$ 1,960	$ 1,881	$ 1,876	$ 1,845	$ 1,795	$ 8,310	$ 7,397	$ 7,244
Depreciation on operating leases	1,313	1,248	1,196	1,100	1,062	1,033	966	951	4,857	4,012	3,568
Interest expense	230	161	215	130	104	386	314	536	736	1,340	940
Net financing revenues	638	703	646	730	715	457	565	308	2,717	2,045	2,736
Other income	203	221	220	188	191	209	157	145
Provision for credit losses	88	103	79	38	68	63	28	11	308	170	121
Expenses	363	329	320	303	327	297	301	298
Income before income taxes	390	492	467	577	511	306	393	144	1,926	1,354	2,155
Provision for income taxes	155	185	176	213	182	113	149	53	729	497	824
Net income	$ 235	$ 307	$ 291	$ 364	$ 329	$ 193	$ 244	$ 91	$ 1,197	$ 857	$ 1,331