ACQUISITIONS - Revenue and income since acquisition date (Details) - Bats Global Markets, Inc. - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Acquisitions
Revenue	$ 470.2	$ 446.0	$ 996.7	$ 605.8
Revenue less cost of revenues	129.0	114.9	260.2	154.1
Operating income (loss)	48.6	28.6	102.5	26.6
Net income (loss)	$ 45.1	$ 18.3	$ 96.2	$ 17.6

Business Combination, Pro Forma Information, Operating Earnings or Loss of Acquiree Since Acquisition Date, Actual

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- Definition

This element represents the amount of revenue less cost of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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- Definition

This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

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