Variable Interest Entities - Summary of Assets and Liabilities of Consolidated Secured Financing VIEs (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Variable Interest Entity [Line Items]
Cash	$ 261	$ 197
Receivables, net	25,933	29,284
Long-term debt	25,278	28,426
Variable Interest Entity [Member]
Variable Interest Entity [Line Items]
Cash	2	6
Receivables, net	3,987	4,197
Total, Consolidated Assets	3,989	4,203
Other liabilities	(40)	(39)
Long-term debt	2,637	2,878
Total, Consolidated Liabilities	$ 2,597	$ 2,839