Variable Interest Entities - Summary of LIHTC Investments and Commitments (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Jan. 31, 2022	Dec. 31, 2021
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Gross investment in LIHTC	$ 707,619		$ 68,635
Accumulated amortization	(56,887)		(25,216)
Net investment in LIHTC	650,732		43,419
Unfunded commitments for LIHTC investments	$ 311,282		$ 11,106
Sterling
Variable Interest Entity [Line Items]
Gross investment in LIHTC		$ 515,600
Unfunded commitments for LIHTC investments		$ 267,300

Amount of investment in qualified affordable housing projects.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=116633289&loc=SL49122993-202985

+ Details

Name:	us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of commitment or contingent commitments to qualified affordable housing project investments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (e)
-URI https://asc.fasb.org/extlink&oid=116633289&loc=SL49122993-202985

+ Details

Name:	us-gaap_QualifiedAffordableHousingProjectInvestmentsCommitment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

No definition available.

+ Details

Name:	us-gaap_VariableInterestEntityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amortization Method Qualified Affordable Housing Project Investments, Accumulated Amortization

+ References

No definition available.

+ Details

Name:	wbs_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAccumulatedAmortization
Namespace Prefix:	wbs_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amortization Method Qualified Affordable Housing Project Investments, Gross Investment

+ References

No definition available.

+ Details

Name:	wbs_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsGrossInvestment
Namespace Prefix:	wbs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	srt_ConsolidatedEntitiesAxis=us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=wbs_SterlingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: