Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]
Maximum credit risk for recourse associated with loans sold under Federal National Mortgage Association Delegated Underwriting and Servicing program	$ 2,400,000,000	$ 2,300,000,000
Period of noncancelable operating lease in years	24 years
Range of reasonably possible losses, minimum	0
Range of reasonably possible losses, maximum	$ 40,000,000