Variable Interest Entities - Schedule of Assets and Liabilities related to Variable Interest Entities Securitization Transactions (Details) - USD ($) $ in Millions	Sep. 30, 2020	Mar. 31, 2020
Variable Interest Entity [Line Items]
Restricted Cash	$ 1,443	$ 1,739
Net Securitized Assets	74,270	73,996
Other Assets	2,605	2,823
Debt	105,902	97,740
Other liabilities	5,188	7,854
Other assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	1,443	996
Net Securitized Assets	24,337	17,961
Other Assets	76	131
Other liabilities [Member]
Variable Interest Entity [Line Items]
Debt	20,480	14,568
Other liabilities	13	12
Retail Finance Receivables [Member] | Other assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	1,034	694
Net Securitized Assets	17,764	12,375
Other Assets	40	5
Retail Finance Receivables [Member] | Other liabilities [Member]
Variable Interest Entity [Line Items]
Debt	15,933	10,933
Other liabilities	12	10
Investments In Operating Leases, Net [Member] | Other assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	409	302
Net Securitized Assets	6,573	5,586
Other Assets	36	126
Investments In Operating Leases, Net [Member] | Other liabilities [Member]
Variable Interest Entity [Line Items]
Debt	4,547	3,635
Other liabilities	$ 1	$ 2