Relationship with Bayview Lending Group LLC and Bayview Financial Holdings, L.P. - Additional Information (Detail) - USD ($)		3 Months Ended
		Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Schedule of Equity Method Investments [Line Items]
Revenue from contract with customer		$ 397,000,000	$ 367,000,000
Loan facility carrying amount	[1]	10,496,000,000		$ 12,605,000,000
Loans and leases (a)	[1]	134,574,000,000		135,581,000,000
Deposits		165,409,000,000		161,095,000,000
Bayview Financial
Schedule of Equity Method Investments [Line Items]
Deposits		3,200,000,000		2,200,000,000
Commercial and industrial
Schedule of Equity Method Investments [Line Items]
Loans and leases (a)		$ 60,596,000,000		61,481,000,000
Bayview Lending Group
Schedule of Equity Method Investments [Line Items]
Ownership percentage (as a percent)		20.00%
Equity method investments		$ 0
Bayview Lending Group | Other Revenues From Operations
Schedule of Equity Method Investments [Line Items]
Income from equity method investments			25,000,000
Bayview Lending Group and Bayview Financial
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of mortgage servicing rights		971,000,000		1,000,000,000.0
Revenue from contract with customer		1,000,000
Bayview Financial
Schedule of Equity Method Investments [Line Items]
Outstanding principal balances of residential mortgage loans from Bayview Financial		161,000,000,000.0		111,500,000,000
Revenues from sub-servicing		40,000,000	$ 32,000,000
Investment securities in held-to-maturity portfolio securitized by Bayview Financial		36,000,000		$ 37,000,000
Bayview Financial | Commercial and industrial
Schedule of Equity Method Investments [Line Items]
Loans and leases (a)		306,000,000
Bayview Financial | Syndicated Loan Facility
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount		2,600,000,000
Bayview Financial | Syndicated Loan Facility | M&T Bank
Schedule of Equity Method Investments [Line Items]
Loan facility carrying amount		$ 394,000,000

[1] Loans and leases of $2.1 billion and $1.5 billion at March 31, 2025 and December 31, 2024, respectively, were held in special purpose trusts to settle the respective obligations of asset-backed notes issued by those trusts. The outstanding balances of those asset-backed notes were included in Long-term borrowings and were $1.8 billion at March 31, 2025 and $1.2 billion at December 31, 2024.