Asset-Backed Securities Issued - Additional Information (Detail) (USD $)	6 Months Ended				6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012 Asset-backed Securities	Jun. 30, 2013 Asset-backed Securities	Dec. 31, 2012 Asset-backed Securities	Jun. 30, 2013 Asset-backed Securities Maximum	Jun. 30, 2013 Asset-backed Securities Contractual maturities of over five years	Jun. 30, 2013 Asset-backed Securities Contractual maturities of one to five years	Jun. 30, 2013 Asset-backed Securities Certificates With Principal Value	Dec. 31, 2012 Asset-backed Securities Certificates With Principal Value	Jun. 30, 2013 Asset-backed Securities Certificates With Principal Value Contractual maturities of over five years	Jun. 30, 2013 Asset-backed Securities Certificates With Principal Value Contractual maturities of one to five years
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.
ABS issued			$ 2,214,296,000	$ 2,529,941,000		$ 2,180,000,000	$ 38,000,000
Principal value								2,228,795,000	2,544,311,000	2,190,000,000	38,000,000
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 deferred ABS issuance costs		$ 1,000,000			$ 1,000,000