Commitments and Contingencies - Commitments and Guarantees (Details) - USD ($) $ in Millions	Mar. 31, 2016	Mar. 31, 2015
Commitments:
Credit facilities commitments with dealers	$ 1,168	$ 1,137
Minimum lease commitments	55	60
Total commitments	1,223	1,197
Total commitments and guarantees	1,323	1,297
Performance Guarantee [Member] | Putnam and Gibson Counties [Member]
Commitments:
Guarantees of affiliate pollution control and solid waste disposal bonds	$ 100	$ 100