Guarantee Arrangements and Pledged Assets and Collateral - Summary of Change in Estimated Repurchase Liability for Loans Sold to GSEs and Other Third Parties (Detail) (Obligation to Repurchase Receivables Sold [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Obligation to Repurchase Receivables Sold [Member]
Estimated Repurchase Liability For Loans Sold [Roll Forward]
Balance at beginning of period	$ 34	$ 217	$ 99	$ 219
Increase (decrease) in liability recorded through earnings	(4)	0	(38)	36
Realized losses	0	(19)	(31)	(57)
Balance at end of period	$ 30	$ 198	$ 30	$ 198