Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Total Revenues	$ 1,522.1	$ 1,179.6
Services transferred at a point in time [Member]
Revenues	1,211.2	892.9
Services transferred over time [Member]
Revenues	307.5	277.7
One-time charges and miscellaneous revenues [Member]
Revenues	3.4	9.0
Clearing and transaction fees [Member]
Revenues	1,278.8	952.6
Clearing and transaction fees [Member] | Interest rate [Member]
Revenues	418.3	302.8
Clearing and transaction fees [Member] | Equities [Member]
Revenues	248.2	145.9
Clearing and transaction fees [Member] | Foreign Exchange [Member]
Revenues	48.2	41.2
Clearing and transaction fees [Member] | Agricultural commodity [Member]
Revenues	117.7	105.0
Clearing and transaction fees [Member] | Energy [Member]
Revenues	221.8	165.0
Clearing and transaction fees [Member] | Metal [Member]
Revenues	78.8	51.0
Clearing and transaction fees [Member] | Cash Markets [Member]
Revenues	124.4	122.9
Clearing and transaction fees [Member] | Interest Rate Swap [Member]
Revenues	21.4	18.8
Market data and information services
Revenues	131.5	130.1
Other
Revenues	$ 111.8	$ 96.9