ACQUISITIONS - Acquisition date fair value of consideration transferred (Details) - USD ($) $ in Millions		6 Months Ended
	Feb. 28, 2017	Jun. 30, 2017
Acquisitions
Cash consideration for Bats outstanding common stock		$ 1,405.4
Bats Global Markets, Inc.
Acquisitions
Cash consideration for Bats outstanding common stock	$ 955.5
Common stock issued	2,387.3
Equity awards issued	37.4
Total consideration paid, excluding debt extinguished	3,380.2
Debt extinguished	580.0
Total consideration	$ 3,960.2