Variable Interest Entities and Asset Securitizations - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Mar. 31, 2024	Dec. 31, 2023
Loss on securitization of assets			$ 0
Asset-backed notes	$ 822,000,000		822,000,000			$ 474,000,000
Loans	132,798,000,000		132,798,000,000			131,939,000,000
Other assets for its "investment" in the common securities recognized by the company of various trusts	22,000,000		22,000,000			22,000,000
Total assets of partnerships in which the company invested	208,855,000,000		208,855,000,000			208,264,000,000
Secured Debt
Asset-backed notes	457,000,000		457,000,000		$ 526,000,000
Long-term debt term (in years)					2 years
Loans and leases average rate					5.29%
Secured Debt | Third Party Investors
Asset-backed notes	446,000,000		446,000,000		$ 511,000,000
Secured Debt | M&T Bank
Asset-backed notes					$ 15,000,000
Variable Interest Entity Primary Beneficiary
Total assets of partnerships in which the company invested	9,500,000,000		9,500,000,000			$ 9,800,000,000
Federal tax credits and other federal tax benefits recognized	8,000,000	$ 10,000,000	15,000,000	$ 16,000,000
Investments amortized to income tax expense	45,000,000	41,000,000	88,000,000	82,000,000
Maximum exposure to loss of investments in real estate partnerships	2,200,000,000		2,200,000,000
Variable Interest Entity Primary Beneficiary | Renewable Energy
Federal tax credits and other federal tax benefits recognized	9,000,000	4,000,000	9,000,000	4,000,000
Investments amortized to income tax expense	$ 20,000,000	$ 12,000,000	$ 20,000,000	$ 12,000,000