Finance Receivables, Net (Credit Quality Indicator) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Current	$ 60,954	$ 58,058
30-59 Days Past Due	560	442
60-89 Days Past Due	114	82
90 Days Past Due	44	29
Total Finance Receivables	61,672	58,611
Wholesale [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	7,879	7,008
30-59 Days Past Due	0	0
60-89 Days Past Due	0	0
90 Days Past Due	0	0
Total Finance Receivables	7,879	7,008
Wholesale [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	7,167	6,249
Wholesale [Member] | Credit Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	664	675
Wholesale [Member] | At Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	39	78
Wholesale [Member] | Default [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	9	6
Real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	4,402	4,361
30-59 Days Past Due	0	0
60-89 Days Past Due	0	0
90 Days Past Due	0	0
Total Finance Receivables	4,402	4,361
Real estate [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	3,872	3,746
Real estate [Member] | Credit Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	495	467
Real estate [Member] | At Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	34	148
Real estate [Member] | Default [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	1	0
Working capital [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	1,675	1,495
30-59 Days Past Due	0	1
60-89 Days Past Due	0	0
90 Days Past Due	0	0
Total Finance Receivables	1,675	1,496
Working capital [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	1,585	1,422
Working capital [Member] | Credit Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	58	61
Working capital [Member] | At Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	25	8
Working capital [Member] | Default [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Finance Receivables	7	5
Retail Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	46,648	44,842
30-59 Days Past Due	550	433
60-89 Days Past Due	113	80
90 Days Past Due	44	28
Total Finance Receivables	47,355	45,383
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	350	352
30-59 Days Past Due	10	8
60-89 Days Past Due	1	2
90 Days Past Due	0	1
Total Finance Receivables	$ 361	$ 363