Acquisition - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended	9 Months Ended
Feb. 22, 2021	Sep. 30, 2021	Sep. 30, 2021
Peoples United Financial Inc
Business Acquisition [Line Items]
Business combination, market value	$ 7,600
Common stock, price per share		$ 149.34	$ 149.34
Assets		$ 63,700	$ 63,700
Loans		39,500	39,500
Deposits		52,900	52,900
Liabilities		55,900	55,900
Stockholders' equity			7,800
Peoples United Financial Inc \| Investment Banking, Legal and Other Services [Member]
Business Acquisition [Line Items]
Merger-related expenses		$ 9	$ 23
MT
Business Acquisition [Line Items]
Common stock, price per share	$ 0.118

Business combination recognized identifiable assets acquisition of deposits.

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- Definition

Business combination recognized identifiable assets acquisition of loans outstanding.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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- Definition

Amount of equity interests of the acquirer, including instruments or interests issued or issuable in consideration for the business combination.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
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-Paragraph 8
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Amount of assets acquired at the acquisition date.

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- Definition

Amount of liabilities due within one year or within the normal operating cycle, if longer, assumed at the acquisition date.

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- Definition

Fair value at acquisition-date of the equity interest in the acquiree held by the acquirer, immediately before the acquisition date for businesses combined in stages.

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- Definition

Amount of expense (income) related to the increase (decrease) in reserve for business combination costs. Includes, but is not limited to, legal, accounting, and other costs incurred to consummate the merger.

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- Definition

Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

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