Transfers of Residential Loans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Residential Loan Transfers [Line Items]
Loans Receivable, Period Past Due	60 days
Loans Pledged As Collateral, Unpaid Principal Balance	$ 9,200,000,000
Residential Loans And Real Estate Owned Pledged As Collateral	9,900,000,000
Residential Loan Transfers Accounted for as Sales [Member]
Residential Loan Transfers [Line Items]
Transferred Residential Loans	$ 86,300,000	$ 9,100,000
Forward Loans Serviced Number Days Past Due Threshold	60 days or more