Acquisition and Divestitures - Additional Information (Details) - USD ($)				9 Months Ended	12 Months Ended
	Apr. 29, 2023	Oct. 30, 2022	Apr. 01, 2022	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Oct. 31, 2022	Dec. 31, 2020
Business Acquisition [Line Items]
ACL for non-PCD loan and leases			$ 242,000,000
Initial estimate of expected credit losses			99,000,000
Goodwill				$ 8,490,000,000	$ 8,465,000,000	$ 8,490,000,000
Revenues					9,643,000,000	8,179,000,000	$ 5,992,000,000
Net income (loss)					2,741,000,000	1,992,000,000	1,859,000,000
Assets				200,730,000,000	208,264,000,000	200,730,000,000
Shareholders’ equity				25,318,000,000	26,957,000,000	25,318,000,000	17,903,000,000		$ 16,187,000,000
Trust Income [Member]
Business Acquisition [Line Items]
Revenue from contract with customer					680,000,000	741,000,000	645,000,000
Collective Investment Trust [Member] | Trust Income [Member]
Business Acquisition [Line Items]
Gain (loss) on sale of subsidiary, pre-tax	$ 225,000,000
Gain (loss) on sale of subsidiary after-tax effect	$ 157,000,000
Revenue from contract with customer					60,000,000	165,000,000	151,000,000
Common Stock [Member]
Business Acquisition [Line Items]
Shareholders’ equity				90,000,000	$ 90,000,000	$ 90,000,000	80,000,000		$ 80,000,000
Minimum [Member]
Business Acquisition [Line Items]
Amortization period					3 years
Maximum [Member]
Business Acquisition [Line Items]
Amortization period					7 years
Peoples United Financial Inc [Member]
Business Acquisition [Line Items]
Business combination, market value			$ 8,400,000,000
Common stock, price per share			$ 164.66
ACL for non-PCD loan and leases			$ 242,000,000
Goodwill			3,908,000,000
Core deposit and other intangible assets			$ 261,000,000
Revenues				1,600,000,000
Net income (loss)				$ 165,000,000
Peoples United Financial Inc [Member] | Financial Service [Member]
Business Acquisition [Line Items]
Merger-related expenses					$ 0
Peoples United Financial Inc [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Common stock issued in transaction			50,325,004
Peoples United Financial Inc [Member] | Core Deposit and Other Intangible Assets [Member] | Minimum [Member]
Business Acquisition [Line Items]
Amortization period			3 years
Peoples United Financial Inc [Member] | Core Deposit and Other Intangible Assets [Member] | Maximum [Member]
Business Acquisition [Line Items]
Amortization period			7 years
M T [Member]
Business Acquisition [Line Items]
Common stock, price per share			$ 0.118
M&T Insurance Agency, Inc [Member]
Business Acquisition [Line Items]
Revenues		$ 34,000,000					$ 37,000,000
Gain (loss) on sale of subsidiary, pre-tax					136,000,000
Gain (loss) on sale of subsidiary after-tax effect					$ 98,000,000
Assets								$ 18,000,000
Shareholders’ equity								$ 6,000,000