Basis of Presentation and Principles of Consolidation (Narrative) (Details) $ / shares in Units, $ in Millions		9 Months Ended
	Mar. 04, 2021	Sep. 30, 2021 USD ($) $ / shares	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Stock split conversion ratio	2
Class A Common Stock, par value (in dollars per share) | $ / shares		$ 0.001
Total equity		$ 6,008.7	$ 5,778.3	$ 5,451.9	$ 5,105.2	$ 4,800.3	$ 4,596.2
Common Stock
Total equity		0.6	0.6	0.6	0.6	0.6	0.6
Common Stock | Stock Split [Member]
Total equity		0.3		0.3	0.3		0.3
Additional Paid in Capital
Total equity		2,289.5	$ 2,198.9	2,068.1	1,937.8	$ 1,834.2	1,683.0
Additional Paid in Capital | Stock Split [Member]
Total equity		$ (0.3)		$ (0.3)	$ (0.3)		$ (0.3)
MTS Test & Simulation
Maximum expected duration of time (in years) to close on the sale of business from the date of the acquisition		1 year