Guarantee Arrangements and Pledged Assets and Collateral - Summary of Change in Estimated Repurchase Liability for Loans Sold to GSEs and Other Third Parties (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Estimated Repurchase Liability For Loans Sold [Roll Forward]
Balance at beginning of period	$ 99	$ 219
Increase (decrease) in liability recorded through earnings	(34)	13
Realized losses	(29)	(21)
Balance at end of period	$ 36	$ 211