Commitments and Contingencies - Commitments and Guarantees (Details) - USD ($) $ in Millions	Mar. 31, 2017	Mar. 31, 2016
Commitments:
Credit facilities commitments with dealers	$ 1,199	$ 1,168
Minimum lease commitments	59	55
Total commitments	1,258	1,223
Total commitments and guarantees	1,358	1,323
Performance Guarantee [Member] | Putnam and Gibson Counties [Member]
Commitments:
Guarantees of affiliate pollution control and solid waste disposal bonds	$ 100	$ 100