Variable Interest Entities - Schedule of Assets and Liabilities related to Variable Interest Entities Securitization Transactions (Details) - USD ($) $ in Millions	Sep. 30, 2019	Mar. 31, 2019
Variable Interest Entity [Line Items]
Restricted Cash	$ 941	$ 985
Net Securitized Assets	72,988	70,517
Other Assets	2,206	1,981
Debt	95,093	92,922
Other liabilities	4,840	4,564
Other assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	941	985
Net Securitized Assets	16,425	16,382
Other Assets	117	192
Other liabilities [Member]
Variable Interest Entity [Line Items]
Debt	12,837	12,401
Other liabilities	11	12
Retail Finance Receivables [Member] | Other assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	669	630
Net Securitized Assets	12,272	11,075
Other Assets	6	6
Retail Finance Receivables [Member] | Other liabilities [Member]
Variable Interest Entity [Line Items]
Debt	10,337	9,202
Other liabilities	9	10
Investments In Operating Leases, Net [Member] | Other assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	272	355
Net Securitized Assets	4,153	5,307
Other Assets	111	186
Investments In Operating Leases, Net [Member] | Other liabilities [Member]
Variable Interest Entity [Line Items]
Debt	2,500	3,199
Other liabilities	$ 2	$ 2