Guarantee Arrangements and Pledged Assets - Trend in Repurchase Demands Received on Loans Sold to GSEs and Other Third Parties by Loan Origination Vintage (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Commitments and Contingencies Disclosure [Abstract]
Pre- 2004	$ 2		$ 2
2004	9		4
2005	4		4
2006	15		16
2007	37		45
2008	23		27
Post 2008	5		4
Total repurchase demands received	$ 95	[1]	$ 102	[1]

[1] Includes repurchase demands on loans sourced from our legacy broker channel of $77 million and $84 million at March 31, 2013 and 2012, respectively.