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Deposits - Narrative (Details) - USD ($) $ in Billions	Dec. 31, 2025	Dec. 31, 2024
Deposits [Abstract]
Time deposits of $250,000 or more	$ 4.0	$ 3.9

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- References

No definition available.

+ Details

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

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- Definition

Time Deposits, $250,000 Or More

+ References

No definition available.

+ Details

Name:	wtfc_TimeDeposits250000OrMore
Namespace Prefix:	wtfc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant