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		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Estimated Repurchase Liability For Loans Sold [Roll Forward]
Balance at beginning of period	$ 217	$ 222	$ 219	$ 237
Increase in liability recorded through earnings	0	28	36	81
Realized losses	(19)	(34)	(57)	(102)
Balance at end of period	$ 198	$ 216	$ 198	$ 216