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
	Mar. 31, 2015	Mar. 31, 2014
Obligation to Repurchase Receivables Sold [Member]
Estimated Repurchase Liability For Loans Sold [Roll Forward]
Balance at beginning of period	$ 27	$ 99
Increase (decrease) in liability recorded through earnings	(3)	(34)
Realized losses	(1)	(29)
Balance at end of period	$ 23	$ 36