Business Segments - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total assets of businesses held for sale	$ 8.2		$ 26.0
KCG Hotspot
Segment Reporting Information [Line Items]
Gain from sale of business		$ 373.8
Corporate and Other | Businesses Held for Sale
Segment Reporting Information [Line Items]
Total assets of businesses held for sale	8.2
Corporate and Other | BATS
Segment Reporting Information [Line Items]
Gain from sale of portion of investment	$ 33.4
Global Execution Services | Revenues | KCG Hotspot
Segment Reporting Information [Line Items]
Gain from sale of business		385.0
Global Execution Services | Pre-tax Earnings | KCG Hotspot
Segment Reporting Information [Line Items]
Gain from sale of business		$ 373.8