Allowance for Credit Losses - Aging of Finance Receivables by Class (Details) - USD ($) $ in Millions	Dec. 31, 2015	Mar. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 1,001	$ 628
Current	65,382	65,939
Total Finance Receivables	66,383	66,567
90 Days or Greater Past Due and Accruing	53	32
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	743	475
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	176	102
90 Days or Greater Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	82	51
Retail Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,001	618
Current	50,206	49,684
Total Finance Receivables	51,207	50,302
90 Days or Greater Past Due and Accruing	53	32
Retail Loan [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	743	467
Retail Loan [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	176	100
Retail Loan [Member] | 90 Days or Greater Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	82	51
Commercial Finance [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		10
Current	0	511
Total Finance Receivables	0	521
90 Days or Greater Past Due and Accruing		0
Commercial Finance [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	8
Commercial Finance [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	2
Commercial Finance [Member] | 90 Days or Greater Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Wholesale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	8,508	9,226
Total Finance Receivables	8,508	9,226
90 Days or Greater Past Due and Accruing	0	0
Wholesale [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Wholesale [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Wholesale [Member] | 90 Days or Greater Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	4,744	4,665
Total Finance Receivables	4,744	4,665
90 Days or Greater Past Due and Accruing	0	0
Real estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Real estate [Member] | 90 Days or Greater Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Working capital [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Current	1,924	1,853
Total Finance Receivables	1,924	1,853
90 Days or Greater Past Due and Accruing	0	0
Working capital [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Working capital [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Working capital [Member] | 90 Days or Greater Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0	$ 0