Allowance for Credit Losses (Past Dues) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012
Past Due Finance Receivables and Investments in Operating Leases
Finance receivables	$ 158	$ 111
Operating leases	38	31
Total	196	142
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	560	442
60-89 Days Past Due	114	82
90 Days Past Due	44	29
Total Past Due	718	553
Current	60,954	58,058
Total Finance Receivables	61,672	58,611
Carrying Amount 90 Days Past Due and Accruing	44	29
Retail Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	550	433
60-89 Days Past Due	113	80
90 Days Past Due	44	28
Total Past Due	707	541
Current	46,648	44,842
Total Finance Receivables	47,355	45,383
Carrying Amount 90 Days Past Due and Accruing	44	28
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	10	8
60-89 Days Past Due	1	2
90 Days Past Due	0	1
Total Past Due	11	11
Current	350	352
Total Finance Receivables	361	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	7,879	7,008
Total Finance Receivables	7,879	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	4,402	4,361
Total Finance Receivables	4,402	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	1,675	1,495
Total Finance Receivables	1,675	1,496
Carrying Amount 90 Days Past Due and Accruing	$ 0	$ 0