Commitments and Contingencies - Additional Information (Detail) - USD ($)		12 Months Ended
	May 12, 2016	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Maximum credit risk for recourse associated with loans sold under Federal National Mortgage Association Delegated Underwriting and Servicing program		$ 2,800,000,000	$ 2,500,000,000
Period of noncancelable operating lease in years		22 years
Payment of litigation settlement expense	$ 64,000,000
Minimum [Member]
Loss Contingencies [Line Items]
Range of reasonably possible losses		$ 0
Maximum [Member]
Loss Contingencies [Line Items]
Range of reasonably possible losses		$ 40,000,000