Litigation and Regulatory Matters - Additional Information (Detail) (USD $)	1 Months Ended	0 Months Ended	1 Months Ended
	Dec. 31, 2013 mortgage_loan	Oct. 17, 2013	Apr. 30, 2015	Mar. 31, 2015
Residential Funding Litigation [Member]
Loss Contingencies [Line Items]
Mortgage loans purchased that resulted in alleged losses	16,000
Securities Litigation [Member]
Loss Contingencies [Line Items]
Litigation judgment claims		$ 2,500,000,000
Claims still open to special court		625,000,000
Possible future expenses related to amount of damages				3,600,000,000
Subsequent Event [Member] | Weller, et. all. v. HSBC Mortgage Services, Inc., et. al. [Member]
Loss Contingencies [Line Items]
Litigation settlement			$ 1,800,000