Guarantee Arrangements and Pledged Assets and Collateral - Trend in Repurchase Demands Received on Loans Sold to GSEs and Other Third Parties by Loan Origination Vintage (Parenthetical) (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
Commitments and Contingencies Disclosure [Abstract]
Repurchase demands received from our legacy broker channel	$ 44	$ 151	$ 120	$ 233