Acquisition and Divestiture - Additional Information (Details) - USD ($)			3 Months Ended		9 Months Ended
	Apr. 29, 2023	Apr. 01, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021
Business Acquisition [Line Items]
Carrying Value			$ 2,010,600,000		$ 2,010,600,000			$ 2,010,600,000
Goodwill			8,465,089,000		8,465,089,000			8,490,089,000
ACL for non-PCD loan and leases		$ 242,000,000
Initial estimate of expected credit losses		99,000,000
Assets			209,124,316,000		209,124,316,000			200,729,841,000
Shareholders' equity			26,196,502,000	$ 25,256,493,000	26,196,502,000	$ 25,256,493,000	$ 25,800,933,000	25,317,990,000	$ 25,794,531,000	$ 17,903,405,000
Net Income (Loss)			689,941,000	646,596,000	2,258,599,000	1,226,292,000
Fiduciary and Trust [Member]
Business Acquisition [Line Items]
Revenue from contract with customer			155,092,000	186,577,000	521,357,000	545,874,000
Collective Investment Trust [Member] | Fiduciary and Trust [Member]
Business Acquisition [Line Items]
Gain (loss) on sale of subsidiary, pre-tax	$ 225,000,000
Revenue from contract with customer					60,000,000	121,000,000
Common Stock [Member]
Business Acquisition [Line Items]
Shareholders' equity			89,718,000	89,718,000	89,718,000	89,718,000	$ 89,718,000	$ 89,718,000	$ 89,718,000	$ 79,871,000
Peoples United Financial Inc [Member]
Business Acquisition [Line Items]
Business combination, market value		$ 8,400,000,000
Common stock, price per share		$ 164.66
Assets		$ 60,244,818,000
Goodwill		3,908,245,000
Core deposits and other intangible assets		$ 261,000,000
Peoples United Financial Inc [Member] | Investment Banking, Legal and Other Services [Member]
Business Acquisition [Line Items]
Merger-related expenses			$ 0	$ 53,000,000	$ 0	$ 293,000,000
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
Peoples United Financial Inc [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Common stock issued in transaction		50,325,004
MT [Member]
Business Acquisition [Line Items]
Common stock, price per share		$ 0.118