Finance Receivables, Net - Aging of Finance Receivables by Class (Details) - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past due	$ 1,025	$ 897
Current	73,936	70,738
Total Finance Receivables	74,961	71,635
90 Days or greater past due and accruing	66	47
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past due	717	657
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past due	203	162
90 Days or Greater Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past due	105	78
Retail Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past due	1,024	892
Current	56,064	53,047
Total Finance Receivables	57,088	53,939
90 Days or greater past due and accruing	66	47
Retail Loan [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past due	717	657
Retail Loan [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past due	203	162
Retail Loan [Member] | 90 Days or Greater Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past due	104	73
Wholesale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past due	0	1
Current	9,826	10,439
Total Finance Receivables	9,826	10,440
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	1
Real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past due	1	0
Current	4,627	4,671
Total Finance Receivables	4,628	4,671
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	1	0
Working capital [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past due	0	4
Current	3,419	2,581
Total Finance Receivables	3,419	2,585
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	$ 4