Allowance for Credit Losses (Past Dues) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Past Due Finance Receivables and Investments in Operating Leases
Finance receivables	$ 119	$ 111
Operating leases	36	31
Total	155	142
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	460	442
60-89 Days Past Due	88	82
90 Days Past Due	31	29
Total Past Due	579	553
Current	62,593	58,058
Total Finance Receivables	63,172	58,611
Carrying Amount 90 Days Past Due and Accruing	31	29
Retail Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	454	433
60-89 Days Past Due	87	80
90 Days Past Due	31	28
Total Past Due	572	541
Current	47,236	44,842
Total Finance Receivables	47,808	45,383
Carrying Amount 90 Days Past Due and Accruing	31	28
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	6	8
60-89 Days Past Due	1	2
90 Days Past Due	0	1
Total Past Due	7	11
Current	362	352
Total Finance Receivables	369	363
Carrying Amount 90 Days Past Due and Accruing	0	1
Wholesale [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	0	0
60-89 Days Past Due	0	0
90 Days Past Due	0	0
Total Past Due	0	0
Current	8,689	7,008
Total Finance Receivables	8,689	7,008
Carrying Amount 90 Days Past Due and Accruing	0	0
Real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	0	0
60-89 Days Past Due	0	0
90 Days Past Due	0	0
Total Past Due	0	0
Current	4,580	4,361
Total Finance Receivables	4,580	4,361
Carrying Amount 90 Days Past Due and Accruing	0	0
Working capital [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	0	1
60-89 Days Past Due	0	0
90 Days Past Due	0	0
Total Past Due	0	1
Current	1,726	1,495
Total Finance Receivables	1,726	1,496
Carrying Amount 90 Days Past Due and Accruing	$ 0	$ 0