Fair Value Measurements (Assets and Liabilities on a Nonrecurring Basis) (Details) - Nonrecurring [Member] - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount of direct investments in privately-held companies, impaired during the period	$ 0.5		$ 2.4
Estimated fair value of direct investments in privately-held companies	0.1		0.4
Other (Expense) Income, Net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment charge	$ 0.4	$ 0.0	$ 2.0	$ 0.9