Commitments and Contingencies - Additional Information (Detail) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Maximum credit risk for recourse associated with loans sold under Federal National Mortgage Association Delegated Underwriting and Servicing program	$ 2,600,000,000	$ 2,500,000,000
Range of reasonably possible losses, minimum	0
Range of reasonably possible losses, maximum	$ 40,000,000