Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P. - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 6,986,186,000	$ 8,444,914,000
Bayview Lending Group [Member]
Schedule of Equity Method Investments [Line Items]
Minority interest in Bayview Lending Group LLC	20.00%
Carrying value of minority interest investment in Bayview Lending Group LLC	$ 0
Bayview Lending Group [Member] | Other Revenues From Operations [Member]
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments	37,000,000	24,000,000	$ 0
Bayview Lending Group and Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of mortgage servicing rights	2,200,000,000	2,500,000,000
Revenue from contract with customer	12,000,000	14,000,000	17,000,000
Bayview Financial [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of residential mortgage loans from Bayview Financial	62,800,000,000	56,800,000,000
Revenues from sub-servicing	125,000,000	114,000,000	$ 103,000,000
Investment securities in held-to-maturity portfolio securitized by Bayview Financial	93,000,000	$ 113,000,000
Bayview Financial [Member] | Syndicated Loan Facility [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	702,000,000
Bayview Financial [Member] | Syndicated Loan Facility [Member] | M&T Bank [Member]
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount	$ 88,000,000