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		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Estimated Repurchase Liability For Loans Sold [Roll Forward]
Balance at beginning of period	$ 211	$ 223	$ 219	$ 237
Increase in liability recorded through earnings	23	32	36	53
Realized losses	(17)	(33)	(38)	(68)
Balance at end of period	$ 217	$ 222	$ 217	$ 222