Variable Interest Entities - Schedule of Assets and Liabilities related to Variable Interest Entities Securitization Transactions (Details) - USD ($) $ in Millions	Dec. 31, 2020	Mar. 31, 2020
Variable Interest Entity [Line Items]
Restricted Cash	$ 1,446	$ 1,739
Net Securitized Assets	78,800	73,996
Other Assets	2,733	2,823
Debt	108,972	97,740
Other liabilities	5,937	7,854
Other assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	1,446	996
Net Securitized Assets	25,602	17,961
Other Assets	100	131
Other liabilities [Member]
Variable Interest Entity [Line Items]
Debt	21,720	14,568
Other liabilities	16	12
Retail Finance Receivables [Member] | Other assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	1,116	694
Net Securitized Assets	19,334	12,375
Other Assets	44	5
Retail Finance Receivables [Member] | Other liabilities [Member]
Variable Interest Entity [Line Items]
Debt	17,367	10,933
Other liabilities	15	10
Investments In Operating Leases, Net [Member] | Other assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	330	302
Net Securitized Assets	6,268	5,586
Other Assets	56	126
Investments In Operating Leases, Net [Member] | Other liabilities [Member]
Variable Interest Entity [Line Items]
Debt	4,353	3,635
Other liabilities	$ 1	$ 2