Capital Structure - Acquisition of KCG (Details) - Class A - USD ($) $ in Millions		1 Months Ended
Jul. 20, 2017	May 31, 2018
Class of Stock [Line Items]
Number of shares of stock issued (in shares)		10,518,750
KCG \| Aranda
Class of Stock [Line Items]
Number of shares of stock issued (in shares)	8,012,821
Aggregate purchase price	$ 125.0
KCG \| North Island Stockholder
Class of Stock [Line Items]
Number of shares of stock issued (in shares)	40,064,103
Aggregate purchase price	$ 618.7

Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

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