Outstanding Balance of Loans Sold by Vintage and Type of Buyer (Detail) (USD $) In Billions, unless otherwise specified	Dec. 31, 2012
Outstanding balance remaining of loans sold to outside investors	$ 108.1
US Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	77.8	[1]
Ginnie Mae
Outstanding balance remaining of loans sold to outside investors	17.5	[1]
Non Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	12.8
Vintage 2005
Outstanding balance remaining of loans sold to outside investors	7.3
Vintage 2005 | US Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	3.1	[1]
Vintage 2005 | Ginnie Mae
Outstanding balance remaining of loans sold to outside investors	0.6	[1]
Vintage 2005 | Non Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	3.6
Vintage 2006
Outstanding balance remaining of loans sold to outside investors	9.3
Vintage 2006 | US Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	3.6	[1]
Vintage 2006 | Ginnie Mae
Outstanding balance remaining of loans sold to outside investors	0.4	[1]
Vintage 2006 | Non Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	5.3
Vintage 2007
Outstanding balance remaining of loans sold to outside investors	11.3
Vintage 2007 | US Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	7.0	[1]
Vintage 2007 | Ginnie Mae
Outstanding balance remaining of loans sold to outside investors	0.4	[1]
Vintage 2007 | Non Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	3.9
Vintage 2008
Outstanding balance remaining of loans sold to outside investors	8.7
Vintage 2008 | US Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	6.8	[1]
Vintage 2008 | Ginnie Mae
Outstanding balance remaining of loans sold to outside investors	1.9	[1]
Vintage 2008 | Non Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	0
Vintage 2009
Outstanding balance remaining of loans sold to outside investors	20.6
Vintage 2009 | US Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	16.4	[1]
Vintage 2009 | Ginnie Mae
Outstanding balance remaining of loans sold to outside investors	4.2	[1]
Vintage 2009 | Non Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	0
Vintage 2010
Outstanding balance remaining of loans sold to outside investors	13.3
Vintage 2010 | US Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	10.1	[1]
Vintage 2010 | Ginnie Mae
Outstanding balance remaining of loans sold to outside investors	3.2	[1]
Vintage 2010 | Non Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	0
Vintage 2011
Outstanding balance remaining of loans sold to outside investors	13.2
Vintage 2011 | US Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	10.7	[1]
Vintage 2011 | Ginnie Mae
Outstanding balance remaining of loans sold to outside investors	2.5	[1]
Vintage 2011 | Non Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	0
Vintage 2012
Outstanding balance remaining of loans sold to outside investors	24.4
Vintage 2012 | US Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	20.1	[1]
Vintage 2012 | Ginnie Mae
Outstanding balance remaining of loans sold to outside investors	4.3	[1]
Vintage 2012 | Non Government Sponsored Agency [Member]
Outstanding balance remaining of loans sold to outside investors	$ 0

[1] Balances based on loans serviced by the Company.