Financial Guarantee Liability - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Guarantor Obligations
Outstanding loan balances	$ 21,500,000,000		$ 21,500,000,000	$ 20,200,000,000
Maximum loss potential	6,300,000,000		6,300,000,000	5,800,000,000
Portion covered by Credit Enhancement Agreement	9,700,000		9,700,000	$ 9,800,000
Provision for expected credit losses	$ 222,000	$ 14,480,000	$ 14,700,000
Fannie Mae DUS or Freddie TAH Loans | Maximum
Guarantor Obligations
Percentage of contingent liability of actual losses incurred on outstanding loans (in percentage)			33.00%