Asset Backed Securities Issued - Additional Information (Detail) (USD $)	3 Months Ended											3 Months Ended
	Mar. 31, 2012	Mar. 31, 2012 Asset-backed Securities	Dec. 31, 2011 Asset-backed Securities	Mar. 31, 2012 Asset-backed Securities Contractual maturities of over five years	Mar. 31, 2012 Asset-backed Securities Contractual maturities of one to five years	Mar. 31, 2012 Asset-backed Securities Certificates With Principal Value	Dec. 31, 2011 Asset-backed Securities Certificates With Principal Value	Mar. 31, 2012 Asset-backed Securities Certificates With Principal Value Contractual maturities of over five years	Mar. 31, 2012 Asset-backed Securities Certificates With Principal Value Contractual maturities of one to five years	Mar. 31, 2012 Asset-backed Securities Sequoia	Dec. 31, 2011 Asset-backed Securities Sequoia	Mar. 31, 2012 Asset-backed Securities Sequoia Maximum	Mar. 31, 2011 Asset-backed Securities Sequoia Maximum	Mar. 31, 2012 Asset-backed Securities Sequoia Certificates With Principal Value	Dec. 31, 2011 Asset-backed Securities Sequoia Certificates With Principal Value	Dec. 31, 2011 Asset-backed Securities Third Party	Jul. 31, 2011 Asset-backed Securities Third Party	Mar. 31, 2012 Asset-backed Securities Resecuritization	Dec. 31, 2011 Asset-backed Securities Resecuritization	Jul. 31, 2011 Asset-backed Securities Resecuritization	Mar. 31, 2012 Asset-backed Securities Resecuritization Certificates With Principal Value	Dec. 31, 2011 Asset-backed Securities Resecuritization Certificates With Principal Value
Debt Instrument [Line Items]
Description of interest rate	Substantially all ABS issued pay variable rates of interest, which are indexed to one, three, or six-month LIBOR.
Securitized loans											$ 671,000,000					$ 640,000,000	$ 245,000,000			$ 365,000,000
ABS issued		3,703,782,000	4,139,355,000	3,700,000,000	48,000,000					3,259,684,000	3,710,423,000							207,173,000	219,551,000
Principal value						6,332,291,000	6,802,412,000	6,300,000,000	48,000,000					3,247,757,000	3,697,894,000						207,173,000	219,551,000
Contractual maturities of ABS (in years)				5 years
Contractual maturities of ABS, minimum (in years)					1 year
Contractual maturities of ABS, maximum (in years)					5 years
Amortization of Sequoia deferred ABS issuance costs												$ 1,000,000	$ 1,000,000