Intangible Assets And Goodwill (Components Of Intangible Assets) (Details) - USD ($) $ in Millions		Jun. 30, 2020	Dec. 31, 2019
Intangible Assets [Line Items]
Intangible assets—other, net		$ 4,931.7	$ 5,117.7
Intangible assets—trading products	[1]	17,175.3	17,175.3
Trade Names [Member]
Intangible Assets [Line Items]
Total intangible assets - other, net		450.0	450.0
Clearing Firm, Market Data And Other Customer Relationships [Member]
Intangible Assets [Line Items]
Assigned Value		5,766.8	5,797.1
Accumulated amortization		(1,481.3)	(1,346.0)
Net book value		4,285.5	4,451.1
Technology-Related Intellectual Property [Member]
Intangible Assets [Line Items]
Assigned Value		171.4	174.3
Accumulated amortization		(56.1)	(46.6)
Net book value		115.3	127.7
Other [Member]
Intangible Assets [Line Items]
Assigned Value		101.1	103.8
Accumulated amortization		(20.2)	(14.9)
Net book value		80.9	88.9
Total Amortizable Intangible Assets [Member]
Intangible Assets [Line Items]
Assigned Value		6,039.3	6,075.2
Accumulated amortization		(1,557.6)	(1,407.5)
Net book value		$ 4,481.7	$ 4,667.7

[1] Trading products represent futures and options products acquired in our business combinations with CBOT Holdings, Inc., NYMEX Holdings, Inc. and The Board of Trade of Kansas City, Missouri, Inc. Clearing and transaction fees are generated through the trading of these products. These trading products, most of which have traded for decades, require authorization from the Commodity Futures Trading Commission (CFTC). Product authorizations from the CFTC have no term limits.