Variable Interest Entities - Schedule of Assets and Liabilities related to Variable Interest Entities Securitization Transactions (Details) - USD ($) $ in Millions	Sep. 30, 2017	Mar. 31, 2017
Variable Interest Entity [Line Items]
Restricted Cash	$ 1,028	$ 1,087
Net Securitized Assets	67,396	68,462
Other Assets	2,043	2,044
Debt	98,223	98,233
Other liabilities	3,922	3,952
Variable Interest Entities Assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	1,008	1,067
Gross Securitized Assets	21,528	19,573
Net Securitized Assets	18,993	17,753
Other Assets	129	87
Variable Interest Entities Liabilities [Member]
Variable Interest Entity [Line Items]
Debt	14,649	14,319
Other liabilities	8	6
Retail Finance Receivables [Member] | Variable Interest Entities Assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	712	856
Gross Securitized Assets	12,423	13,071
Net Securitized Assets	12,219	12,865
Other Assets	6	7
Retail Finance Receivables [Member] | Variable Interest Entities Liabilities [Member]
Variable Interest Entity [Line Items]
Debt	10,232	11,017
Other liabilities	6	5
Investments In Operating Leases, Net [Member] | Variable Interest Entities Assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	296	211
Gross Securitized Assets	9,105	6,502
Net Securitized Assets	6,774	4,888
Other Assets	123	80
Investments In Operating Leases, Net [Member] | Variable Interest Entities Liabilities [Member]
Variable Interest Entity [Line Items]
Debt	4,417	3,302
Other liabilities	$ 2	$ 1