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	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Obligation to Repurchase Receivables Sold [Member]
Estimated Repurchase Liability For Loans Sold [Roll Forward]
Balance at beginning of period	$ 99	$ 219	$ 237
Increase (decrease) in liability recorded through earnings	(41)	21	134
Realized losses	(31)	(141)	(152)
Balance at end of period	$ 27	$ 99	$ 219