Relationship with BLG and Bayview Financial - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 11,450,000,000		$ 8,201,000,000
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	$ 25,000,000	$ 20,000,000
Bayview Lending Group and Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of mortgage servicing rights	1,100,000,000		1,200,000,000
Revenue from contract with customer	1,000,000	2,000,000
Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of residential mortgage loans from Bayview Financial	112,000,000,000		115,300,000,000
Revenues from sub-servicing	32,000,000	$ 32,000,000
Investment securities in held-to-maturity portfolio securitized by Bayview Financial	41,000,000		$ 42,000,000
Bayview Financial [Member] | Syndicated Loan Facility [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	3,700,000,000
Bayview Financial [Member] | Syndicated Loan Facility [Member] | M&T Bank [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 674,000,000