Fair Value Measurements Equity Investments and Other Financial Instruments - Equity Investment Without Readily Determinable Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity Securities without Readily Determinable Fair Value [Roll Forward]
Carrying amount at the beginning of period	$ 7.5	$ 7.5	$ 0.0
Purchases	2.6	0.0	7.5
Impairments or downward adjustments	0.0	0.0	0.0
Upward adjustments	15.1	0.0	0.0
Currency translation on investments	0.2	0.0	0.0
Carrying amount at the end of period	25.4	$ 7.5	$ 7.5
Equity investments, cumulative upward price adjustment	15.1
Additional investment	$ 5.7