Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues
Total Revenues	$ 1,182.3	$ 1,272.7	$ 2,704.4	$ 2,452.3
Expenses
Compensation and benefits	217.0	227.3	424.5	457.6
Technology	49.1	48.6	96.8	95.7
Professional fees and outside services	51.2	41.7	92.9	81.1
Amortization of purchased intangibles	76.6	76.1	153.9	156.8
Depreciation and amortization	36.7	46.3	72.0	79.2
Licensing and other fee agreements	55.4	44.8	129.3	85.3
Other	58.8	89.3	137.6	167.0
Total Expenses	544.8	574.1	1,107.0	1,122.7
Operating Income	637.5	698.6	1,597.4	1,329.6
Non-Operating Income (Expense)
Investment income	32.1	139.3	128.0	318.0
Interest and other borrowing costs	(41.9)	(45.1)	(82.8)	(93.2)
Equity in net earnings of unconsolidated subsidiaries	48.8	43.8	100.0	84.3
Other non-operating income (expense)	(15.2)	(134.5)	(92.0)	(296.4)
Total Non-Operating Income (Expense)	23.8	3.5	53.2	12.7
Income before Income Taxes	661.3	702.1	1,650.6	1,342.3
Income tax provision	158.0	187.5	380.5	331.8
Net Income	503.3	514.6	1,270.1	1,010.5
Less: net (income) loss attributable to non-controlling interests	0.0	(0.8)	(0.6)	0.2
Net Income Attributable to CME Group	$ 503.3	$ 513.8	$ 1,269.5	$ 1,010.7
Earnings per Common Share Attributable to CME Group:
Basic (in dollars per share)	$ 1.41	$ 1.44	$ 3.55	$ 2.83
Diluted (in dollars per share)	$ 1.40	$ 1.43	$ 3.54	$ 2.82
Weighted Average Number of Common Shares:
Basic (in shares)	357,691	357,060	357,607	356,973
Diluted (in shares)	358,457	358,155	358,453	358,103
Clearing and transaction fees [Member]
Revenues	$ 940.2	$ 1,051.8	$ 2,219.0	$ 2,004.4
Market data and information services
Revenues	134.7	128.3	266.2	258.4
Other
Revenues	$ 107.4	$ 92.6	$ 219.2	$ 189.5