Guarantee Arrangements and Pledged Assets and Collateral - Outstanding Repurchase Demands Received From GSEs and Other Third Parties (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Commitments and Contingencies Disclosure [Abstract]
Outstanding repurchase demands on loans sourced from our legacy broker channel	$ 40	$ 65