Variable Interest Entities - Schedule of Assets and Liabilities related to Variable Interest Entities Securitization Transactions (Details) - USD ($) $ in Millions	Sep. 30, 2018	Mar. 31, 2018
Variable Interest Entity [Line Items]
Restricted Cash	$ 991	$ 1,219
Net Securitized Assets	69,328	69,647
Other Assets	1,515	1,614
Debt	98,228	98,353
Other liabilities	4,405	3,987
Other assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	969	1,026
Gross Securitized Assets	22,254	19,999
Net Securitized Assets	19,215	17,633
Other Assets	164	125
Other liabilities [Member]
Variable Interest Entity [Line Items]
Debt	14,529	13,638
Other liabilities	12	10
Retail Finance Receivables [Member] | Other assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	625	729
Gross Securitized Assets	11,863	12,130
Net Securitized Assets	11,658	11,927
Other Assets	6	7
Retail Finance Receivables [Member] | Other liabilities [Member]
Variable Interest Entity [Line Items]
Debt	9,613	9,958
Other liabilities	8	7
Investments In Operating Leases, Net [Member] | Other assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	344	297
Gross Securitized Assets	10,391	7,869
Net Securitized Assets	7,557	5,706
Other Assets	158	118
Investments In Operating Leases, Net [Member] | Other liabilities [Member]
Variable Interest Entity [Line Items]
Debt	4,916	3,680
Other liabilities	$ 4	$ 3