Fair Value Measurements (Assets Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs) (Details) - Fair Value, Nonrecurring - Significant Unobservable Inputs (Level 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities without readily determinable fair value, carrying value	$ 2.4	$ 2.8
Equity securities without readily determinable fair value, after impairment	0.4	1.9
Other income (expense), net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustments to direct investments in privately-held companies	$ 2.0	$ 0.9