Loans and Leases (Interest Income From Impaired Loans And Leases, By Class) (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	$ 248,054	$ 264,162	$ 305,015
Accrued Interest Income	7,192	8,065	8,557
Cash Basis Interest Income	2,310	2,185	2,238
Asset Based Loans [Member]
Financing Receivable, Impaired [Line Items]
Cash Basis Interest Income	0	0	0
Residential Portfolio Segment [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	116,859	126,936	138,215
Accrued Interest Income	4,138	4,377	4,473
Cash Basis Interest Income	1,264	1,200	1,139
Consumer Portfolio Segment [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment			49,337
Accrued Interest Income			1,451
Cash Basis Interest Income			1,099
Consumer Portfolio Segment [Member] \| Home Equity Loan [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	45,578	47,072
Accrued Interest Income	1,323	1,361
Cash Basis Interest Income	1,046	985
Commercial Portfolio Segment [Member] \| Commercial and Industrial Sector [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	62,459	54,708	46,379
Accrued Interest Income	1,095	1,540	1,319
Cash Basis Interest Income	0	0	0
Commercial Portfolio Segment [Member] \| Asset Based Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	295	0	0
Accrued Interest Income	0	0	0
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment			64,495
Accrued Interest Income			1,165
Cash Basis Interest Income	0	0	0
Commercial Real Estate Portfolio Segment [Member] \| Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	17,397	28,451
Accrued Interest Income	417	511
Commercial Real Estate Portfolio Segment [Member] \| Construction Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	594	3,574	6,062
Accrued Interest Income	12	92	133
Cash Basis Interest Income	0	0	0
Finance Leases Portfolio Segment [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	4,872	3,421	527
Accrued Interest Income	207	184	16
Cash Basis Interest Income	$ 0	$ 0	$ 0

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.

No definition available.

+ Details

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

- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_EquitySecuritiesByIndustryAxis=wbs_AssetBasedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EquitySecuritiesByIndustryAxis=us-gaap_CommercialAndIndustrialSectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_RealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_FinanceLeasesPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: