Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)		3 Months Ended
		Mar. 31, 2025	Mar. 31, 2024	Feb. 28, 2025	Dec. 31, 2024
Loss on securitization of assets		$ 0
Financing receivable, accrued interest, before allowance for credit loss		603,000,000			$ 628,000,000
Long-term borrowings (a)	[1]	10,496,000,000			12,605,000,000
Other assets for its "investment" in the common securities recognized by the company of various trusts		16,000,000			17,000,000
Total assets of partnerships in which the company invested		210,321,000,000			208,105,000,000
Variable Interest Entity Primary Beneficiary
Total assets of partnerships in which the company invested		10,600,000,000			10,500,000,000
Federal tax credits and other federal tax benefits recognized		9,000,000	$ 7,000,000
Investments amortized to income tax expense		44,000,000	$ 43,000,000
Maximum exposure to loss of investments in real estate partnerships		2,100,000,000
Variable Interest Entity Primary Beneficiary | Third Party Investors
Long-term borrowings (a)		1,800,000,000
Variable Interest Entity Primary Beneficiary | M&T Bank
Financing receivable, accrued interest, before allowance for credit loss		2,100,000,000			$ 1,500,000,000
Variable Interest Entity Primary Beneficiary | Renewable Energy
Federal tax credits and other federal tax benefits recognized		6,000,000
Investments amortized to income tax expense		$ 11,000,000
Subsidiaries | Secured Debt | 4.874% Asset-Backed Notes
Asset-backed notes (a)				$ 767,000,000
Long-term debt term (in years)				2 years
Loans and leases average rate				4.74%
Subsidiaries | Secured Debt | Third Party Investors | 4.874% Asset-Backed Notes
Asset-backed notes (a)				$ 746,000,000

[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.