Stockholder's Equity - Redemptions and Exchange of LLC Interests (Details) - shares	Sep. 30, 2020	Sep. 30, 2019	Apr. 08, 2019
Tradeweb Markets LLC
Subsidiary, Sale of Stock [Line Items]
Number of LLC Interests held by Tradeweb Markets Inc.	17.40%	35.70%
Ownership interest	82.60%	64.30%	64.30%
Tradeweb Markets LLC | Public Investors
Subsidiary, Sale of Stock [Line Items]
Number of LLC Interests held by Tradeweb Markets Inc.	40.00%
Tradeweb Markets LLC | Bank Stockholders
Subsidiary, Sale of Stock [Line Items]
Number of LLC Interests held by Tradeweb Markets Inc.	7.20%
Tradeweb Markets Inc | Public Investors
Subsidiary, Sale of Stock [Line Items]
Voting power percentage	6.50%
Tradeweb Markets Inc | Bank Stockholders
Subsidiary, Sale of Stock [Line Items]
Voting power percentage	8.40%
Tradeweb Markets Inc | Class A Common Stock | Public Investors
Subsidiary, Sale of Stock [Line Items]
Number of share owned (in shares)	90,985,582
Tradeweb Markets Inc | Class D Common Stock | Bank Stockholders
Subsidiary, Sale of Stock [Line Items]
Number of share owned (in shares)	11,285,182
Tradeweb Markets Inc | Class C Common Stock | Bank Stockholders
Subsidiary, Sale of Stock [Line Items]
Number of share owned (in shares)	5,109,991
Refinitiv | Tradeweb Markets LLC
Subsidiary, Sale of Stock [Line Items]
Ownership interest	52.70%
Refinitiv | Tradeweb Markets Inc
Subsidiary, Sale of Stock [Line Items]
Ownership interest	85.10%
Refinitiv | Tradeweb Markets Inc | Class B Common Stock
Subsidiary, Sale of Stock [Line Items]
Number of share owned (in shares)	96,933,192
Refinitiv | Tradeweb Markets Inc | Class D Common Stock
Subsidiary, Sale of Stock [Line Items]
Number of share owned (in shares)	22,988,329