Changes in the Servicing Assets (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Servicing Assets at Fair Value
Carrying amount as of the beginning of the period	$ 1,358	$ 1,239
Servicing Obligations From Transfers	150	190
Servicing Asset At Amortized Value Amortization	(105)	(86)
Carrying amount before valuation allowance	1,409	1,343
Valuation allowance for servicing assets:
Beginning balance	(661)	(558)
Servicing impairment	151	(49)
Ending balance	(510)	(607)
Carrying amount as of the end of the period	899	736
Automobile Loan Securitizations
Servicing Assets at Fair Value
Servicing Obligations From Transfers	$ 6