Nominal or face amount used to calculate payment on derivative.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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-Section 50
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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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- Definition

Describes the form and magnitude of the award the plaintiff seeks in the legal matter, which may include an unspecified amount of money.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Number of plaintiffs that have filed claims pertaining to a loss contingency.

+ References

No definition available.

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- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

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- Definition

The cash inflow from sales of loans that are secured with real estate mortgages and are held with the intention to resell in the near future.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

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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 http://asc.fasb.org/extlink&oid=116633289&loc=SL49122993-202985

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- Definition

Commitments and contingencies [Line Items].

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No definition available.

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- Definition

Customer balances maintained by clearing broker and subject to indemnification.

+ References

No definition available.

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Balance Type:	credit
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- Definition

Liability for loss indemnification claims on residential mortgage loans previously sold to investors.

+ References

No definition available.

+ Details

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Namespace Prefix:	wtfc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

Losses charged against indemnification liability

+ References

No definition available.

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Namespace Prefix:	wtfc_
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Balance Type:	debit
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- Definition

Unfunded Commitments To Invest In Partnerships

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Commitments and Contingencies (Details) $ in Thousands			12 Months Ended
Commitments and Contingencies (Details) $ in Thousands	Apr. 30, 2020	Oct. 17, 2018 plaintiff	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Commitments And Contingencies [Line Items]
Letters of credit outstanding			$ 348,200	$ 291,800
Mortgage loans sold			7,624,799	4,484,838	$ 4,076,887
Liability for estimated losses on repurchase and indemnification claims			800	2,400
Losses charged against liability			187	639
Unfunded commitments to investment partnerships			28,500
Commitments to invest in partnership for tax credits			178
Customer balances maintained by clearing broker and subject to indemnification			16,800
Northbrook Bank Matter
Commitments And Contingencies [Line Items]
Number of plaintiffs \| plaintiff		2
Damages sought		6 million
Wintrust Bank Matter
Commitments And Contingencies [Line Items]
Damages sought	3.8 billion
Forward contracts
Commitments And Contingencies [Line Items]
Derivative instrument, contractual amounts			2,300,000	837,200
Commercial, commercial real estate, and construction loans \| Commitments to extend credit
Commitments And Contingencies [Line Items]
Commitments to fund			6,400,000	5,100,000
Unused home equity lines \| Commitments to extend credit
Commitments And Contingencies [Line Items]
Commitments to fund			756,200	800,600
Residential real estate \| Commitments to extend credit
Commitments And Contingencies [Line Items]
Commitments to fund			$ 1,700,000	$ 595,100