Fair Value Measurements, Equity Investments and Other Financial Instruments - Equity Investment Without Readily Determinable Fair Value (Details) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($) investment	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Equity Securities without Readily Determinable Fair Value [Roll Forward]
Carrying value at the beginning of period					$ 25.4	$ 7.5	$ 7.5
Purchases					14.7		2.6
Impairments or downward adjustments					0.0		0.0
Upward adjustments	$ 6.6			$ 0.0	6.6	0.0	15.1
Currency translation on investments					(0.6)		0.2
Carrying value at the end of period	46.1		$ 25.4		46.1		25.4
Cumulative upward adjustment	$ 21.7		$ 15.1		21.7		$ 15.1
Number of investments | investment			1
Additional investment		$ 9.0	$ 5.7		$ 16.0	$ 0.0