Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P. - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 5,458,885,000		$ 5,458,885,000			$ 6,986,186,000
Bayview Lending Group [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value of minority interest investment in Bayview Lending Group LLC	0		0
Income (loss) from equity method investments	0	$ 0
Bayview Lending Group [Member] | Other Revenues From Operations [Member]
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments			23,000,000	$ 37,000,000
Bayview Lending Group and Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of mortgage servicing rights	2,000,000,000.0		2,000,000,000.0			2,200,000,000
Revenue from contract with customer	2,000,000	3,000,000	7,000,000	9,000,000
Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of residential mortgage loans from Bayview Financial	67,000,000,000.0		67,000,000,000.0			62,800,000,000
Revenues from sub-servicing	30,000,000	$ 33,000,000	101,000,000	$ 90,000,000
Investment securities in held-to-maturity portfolio securitized by Bayview Financial	80,000,000		80,000,000			$ 93,000,000
Secured loan facilities carrying amount					$ 100,000,000
Outstanding balance of secured debt	87,000,000		87,000,000
Bayview Financial [Member] | Syndicated Loan Facility [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	1,000,000,000.0		1,000,000,000.0
Bayview Financial [Member] | Syndicated Loan Facility [Member] | M&T Bank [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 164,000,000		$ 164,000,000