Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P. - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 7,123,426,000		$ 7,123,426,000		$ 3,964,537,000
Bayview Lending Group [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value of minority interest investment in Bayview Lending Group LLC	$ 0		$ 0
Minority interest in Bayview Lending Group LLC	20.00%		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	$ 0	$ 20,000,000	$ 30,000,000
Bayview Lending Group and Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of mortgage servicing rights	1,200,000,000		1,200,000,000		1,400,000,000
Revenue from contract with customer	1,000,000	3,000,000	5,000,000	7,000,000
Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of residential mortgage loans from Bayview Financial	114,600,000,000		114,600,000,000		96,000,000,000
Revenues from sub-servicing	30,000,000	$ 33,000,000	94,000,000	$ 119,000,000
Investment securities in held-to-maturity portfolio securitized by Bayview Financial	44,000,000		44,000,000		$ 50,000,000
Bayview Financial [Member] | Syndicated Loan Facility [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	3,100,000,000		3,100,000,000
Bayview Financial [Member] | Syndicated Loan Facility [Member] | M&T Bank [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 765,000,000		$ 765,000,000