Fair Value Measurements (Debt Instruments) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2026 USD ($)
$750.0 million Fixed Rate Notes Due September 2043, stated rate of 5.30% [Member]
Debt Instrument, Face Amount	$ 750.0
Debt Instrument, Maturity Date	Sep. 15, 2043
$700.0 Million Fixed Rate Notes Due June 2048, stated rate of 4.15% [Member] [Domain] [Domain]
Debt Instrument, Face Amount	$ 700.0
Debt Instrument, Maturity Date	Jun. 15, 2048
$750.0 Million Fixed Rate Notes Due March 2032, Interest Equal To 2.65%
Debt Instrument, Face Amount	$ 750.0
Debt Instrument, Maturity Date	Mar. 15, 2032
$500.0 Million Fixed Rate Notes Due June 2028, stated rate of 3.75% [Member] [Domain]
Debt Instrument, Face Amount	$ 750.0
Debt Instrument, Maturity Date	Mar. 15, 2030
$750.0 Million Fixed Rate Notes Due March 2025, stated rate of 3.00% [Member]
Debt Instrument, Face Amount	$ 750.0
Debt Instrument, Maturity Date	Mar. 15, 2025
Fair Value, Inputs, Level 2 [Member] \| $750.0 million Fixed Rate Notes Due September 2043, stated rate of 5.30% [Member]
Debt Instrument, Fair Value Disclosure	$ 732.6
Debt Instrument, Face Amount	$ 750.0
Debt Instrument, Maturity Date	Sep. 15, 2043
Fair Value, Inputs, Level 2 [Member] \| $700.0 Million Fixed Rate Notes Due June 2048, stated rate of 4.15% [Member] [Domain] [Domain]
Debt Instrument, Fair Value Disclosure	$ 571.8
Debt Instrument, Face Amount	$ 700.0
Debt Instrument, Maturity Date	Jun. 15, 2048
Fair Value, Inputs, Level 2 [Member] \| $750.0 Million Fixed Rate Notes Due March 2032, Interest Equal To 2.65%
Debt Instrument, Fair Value Disclosure	$ 679.9
Fair Value, Inputs, Level 2 [Member] \| $500.0 Million Fixed Rate Notes Due June 2028, stated rate of 3.75% [Member] [Domain]
Debt Instrument, Fair Value Disclosure	496.1
Debt Instrument, Face Amount	$ 500.0
Debt Instrument, Maturity Date	Jun. 15, 2028
Fair Value, Inputs, Level 2 [Member] \| $750.0 Million Fixed Rate Notes Due March 2025, stated rate of 3.00% [Member]
Debt Instrument, Face Amount	$ 750.0
Debt Instrument, Maturity Date	Mar. 15, 2025
Fair Value, Inputs, Level 2 [Member] \| $750.0 Million Fixed Rate Notes Due March 2030, Interest Equal to 4.4%
Debt Instrument, Fair Value Disclosure	$ 751.4

CME GROUP INC. 10-Q