Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Balance			$ 26,486.9
Other comprehensive income (loss), net of tax	$ 120.2	$ (8.9)	150.9	$ (39.4)
Balance	27,739.0		27,739.0
Investment Securities [Member]
Balance			(0.3)	(0.4)
Other comprehensive income (loss) before reclassifications and income tax benefit (expense)			0.1	0.0
Amounts reclassified from accumulated other comprehensive income (loss)			0.0	0.0
Income tax benefit (expense)			0.0	0.0
Other comprehensive income (loss), net of tax			0.1	0.0
Balance	(0.2)	(0.4)	(0.2)	(0.4)
Defined Benefit Plans [Member]
Balance			(14.1)	(23.4)
Other comprehensive income (loss) before reclassifications and income tax benefit (expense)			(1.2)	(5.9)
Amounts reclassified from accumulated other comprehensive income (loss)			(0.1)	0.0
Income tax benefit (expense)			0.3	1.5
Other comprehensive income (loss), net of tax			(1.0)	(4.4)
Balance	(15.1)	(27.8)	(15.1)	(27.8)
Cash Flow Hedging
Balance			59.3	62.0
Other comprehensive income (loss) before reclassifications and income tax benefit (expense)			0.0	0.0
Amounts reclassified from accumulated other comprehensive income (loss)			(2.0)	(1.8)
Income tax benefit (expense)			0.5	0.4
Other comprehensive income (loss), net of tax			(1.5)	(1.4)
Balance	57.8	60.6	57.8	60.6
Foreign Currency Translation [Member]
Balance			(150.4)	(93.8)
Other comprehensive income (loss) before reclassifications and income tax benefit (expense)			164.3	(33.6)
Amounts reclassified from accumulated other comprehensive income (loss)			0.0	0.0
Income tax benefit (expense)			(11.0)	0.0
Other comprehensive income (loss), net of tax			153.3	(33.6)
Balance	2.9	(127.4)	2.9	(127.4)
Accumulated Other Comprehensive Income (Loss) [Member]
Balance			(105.5)	(55.6)
Other comprehensive income (loss) before reclassifications and income tax benefit (expense)			163.2	(39.5)
Amounts reclassified from accumulated other comprehensive income (loss)			(2.1)	(1.8)
Income tax benefit (expense)			(10.2)	1.9
Other comprehensive income (loss), net of tax			150.9	(39.4)
Balance	$ 45.4	$ (95.0)	$ 45.4	$ (95.0)

CME GROUP INC. 10-Q