Organization (Details) - USD ($) $ / shares in Units, $ in Billions	Apr. 08, 2019	Sep. 30, 2020	Sep. 30, 2019	Apr. 03, 2019
Class A Common Stock
Common Stock, par value (in dollars per share)		$ 0.00001		$ 0.00001
Class B Common Stock
Shares issued (in shares)	96,933,192
Common Stock, par value (in dollars per share)		0.00001		0.00001
Shares contributed by Refinitiv Owner (in shares)	96,933,192
Class C Common Stock
Common Stock, par value (in dollars per share)		0.00001		0.00001
Shares issued to acquire TWM LLC (in shares)	20,000,000
Number of shares canceled (in shares)	9,993,731
Class D Common Stock
Common Stock, par value (in dollars per share)		$ 0.00001		$ 0.00001
Shares issued to acquire TWM LLC (in shares)	105,289,005
Number of shares canceled (in shares)	36,006,269
Tradeweb Markets LLC
Ownership interest	64.30%	82.60%	64.30%
Number of LLC Interests held by Tradeweb Markets Inc.		17.40%	35.70%
Public offering price (in dollars per share)	$ 27.00
Net proceeds	$ 1.2
Initial Public Offering | Class A Common Stock
Shares issued (in shares)	46,000,000
Common Stock, par value (in dollars per share)	$ 0.00001
Public offering price (in dollars per share)	$ 27.00
Underwriter | Class A Common Stock
Shares issued (in shares)	6,000,000