Transfers of Residential Loans - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Residential Loan Transfers Accounted for as Sales [Member]
Residential Loan Transfers [Line Items]
Transferred residential loans	$ 112,600,000	$ 86,300,000
Forward loans serviced number of days past due threshold	60 days or more
Residential Loans Transfers Accounted for as Secured Borrowings [Member]
Residential Loan Transfers [Line Items]
Loans pledged as collateral, unpaid principal balance	9,500,000,000
Residential loans and real estate owned pledged as collateral	$ 10,200,000,000