Finance Receivables, Net (Finance Receivable Credit Quality Indicators) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Mar. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Current	$ 70,788	$ 69,979
Financing receivables, past due	895	836
Total Finance Receivables	71,683	70,815
Retail Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	52,928	52,559
Financing receivables, past due	895	836
Total Finance Receivables	53,823	53,395
Wholesale [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	10,963	10,513
Financing receivables, past due	0	0
Total Finance Receivables	10,963	10,513
Wholesale [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	9,769	9,451
Wholesale [Member] | Credit Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	1,084	946
Wholesale [Member] | At Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	106	75
Wholesale [Member] | Default [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	4	41
Real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	4,588	4,630
Financing receivables, past due	0	0
Total Finance Receivables	4,588	4,630
Real estate [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	4,019	4,070
Real estate [Member] | Credit Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	524	484
Real estate [Member] | At Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	45	29
Real estate [Member] | Default [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	0	47
Working capital [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	2,309	2,277
Financing receivables, past due	0	0
Total Finance Receivables	2,309	2,277
Working capital [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	2,140	2,118
Working capital [Member] | Credit Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	117	105
Working capital [Member] | At Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	52	33
Working capital [Member] | Default [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	0	21
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	642	613
30-59 Days Past Due [Member] | Retail Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	642	613
30-59 Days Past Due [Member] | Wholesale [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	0	0
30-59 Days Past Due [Member] | Real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	0	0
30-59 Days Past Due [Member] | Working capital [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	0	0
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	186	158
60-89 Days Past Due [Member] | Retail Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	186	158
60-89 Days Past Due [Member] | Wholesale [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	0	0
60-89 Days Past Due [Member] | Real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	0	0
60-89 Days Past Due [Member] | Working capital [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	0	0
90 Days or Greater Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	67	65
90 Days or Greater Past Due [Member] | Retail Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	67	65
90 Days or Greater Past Due [Member] | Wholesale [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	0	0
90 Days or Greater Past Due [Member] | Real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	0	0
90 Days or Greater Past Due [Member] | Working capital [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables, past due	$ 0	$ 0