Variable Interest Entities - Summary of Assets and Liabilities of Consolidated Secured Financing VIEs (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Variable Interest Entity [Line Items]
Cash	$ 131		$ 157
Credit loss reserves	(341)	$ (408)	(2,217)	$ (2,463)	$ (2,692)	$ (3,273)
Total receivables, net	9,434		21,242
Long-term debt	12,206		16,427
Variable Interest Entity [Member]
Variable Interest Entity [Line Items]
Cash	0		2
Real estate secured receivables	1,846		2,999
Accrued interest income and other	74		133
Credit loss reserves	(180)		(337)
Total receivables, net	1,740		2,795
Total, Consolidated Assets	1,740		2,797
Other liabilities	(25)		(35)
Long-term debt	943		1,489
Total, Consolidated Liabilities	$ 918		$ 1,454