Variable Interest Entities - Schedule of Variable Interest Entities, Securitization Transactions Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2015	Mar. 31, 2015
Variable Interest Entity [Line Items]
Restricted Cash	$ 826	$ 784
Net Securitized Assets	65,022	65,893
Other assets	4,234	2,282
Debt	95,097	90,231
Other liabilities	3,503	3,355
Variable Interest Entities Securitized Assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	825	784
Gross Securitized Assets	16,113	13,253
Net Securitized Assets	15,562	12,702
Other assets	30	15
Related Liabilities [Member]
Variable Interest Entity [Line Items]
Debt	13,264	10,837
Other liabilities	3	3
Retail Finance Receivables [Member] | Variable Interest Entities Securitized Assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	771	730
Gross Securitized Assets	14,871	11,682
Net Securitized Assets	14,659	11,509
Other assets	5	4
Retail Finance Receivables [Member] | Related Liabilities [Member]
Variable Interest Entity [Line Items]
Debt	12,656	9,980
Other liabilities	3	3
Investments In Operating Leases, Net [Member] | Variable Interest Entities Securitized Assets [Member]
Variable Interest Entity [Line Items]
Restricted Cash	54	54
Gross Securitized Assets	1,242	1,571
Net Securitized Assets	903	1,193
Other assets	25	11
Investments In Operating Leases, Net [Member] | Related Liabilities [Member]
Variable Interest Entity [Line Items]
Debt	608	857
Other liabilities	$ 0	$ 0