Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P. - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 3,498,503,000		$ 4,382,193,000
Bayview Lending Group [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value of minority interest investment in Bayview Lending Group LLC	$ 0
Minority interest in Bayview Lending Group LLC	20.00%
Bayview Lending Group [Member] | Other Revenues From Operations [Member]
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments	$ 0	$ 23,000,000
Bayview Lending Group and Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of mortgage servicing rights	1,900,000,000		1,900,000,000
Revenue from contract with customer	2,000,000	3,000,000
Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of residential mortgage loans from Bayview Financial	69,700,000,000		68,100,000,000
Revenues from sub-servicing	34,000,000	$ 37,000,000
Investment securities in held-to-maturity portfolio securitized by Bayview Financial	73,000,000		$ 77,000,000
Bayview Financial [Member] | FHA Guaranteed Mortgage Loans [Member]
Schedule of Equity Method Investments [Line Items]
FHA guaranteed purchase amount of delinquent loan	1,000,000,000.0
FHA guaranteed mortgage loan	965,000,000
Bayview Financial [Member] | Syndicated Loan Facility [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	1,100,000,000
Bayview Financial [Member] | Syndicated Loan Facility [Member] | M&T Bank [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 139,000,000