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Significant Accounting Policies - Income Tax (Details) - Tradeweb Markets LLC	12 Months Ended
	Dec. 31, 2018 USD ($)
Entity Information [Line Items]
Federal statutory income tax rate	21.00%
Remeasurement of deferred tax asset	$ (1,982,000)
Adjustment to previously recorded provisional tax expense	$ 0

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Amount of income tax expense for remeasurement of deferred tax asset from change in tax rate pursuant to Tax Cuts and Jobs Act of 2017.

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Amount of income tax expense (benefit) from effect of Tax Cuts and Jobs Act of 2017.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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-Topic 740
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