Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (41.7)	$ (122.2)	$ (36.9)	$ (376.4)
Other comprehensive income (loss), net of tax:
Change in foreign currency translation adjustment	(20.1)	31.7	(24.6)	19.0
Net change in unrealized gains (losses) on available-for-sale marketable debt securities		(0.4)	(0.1)
Other comprehensive income (loss), net of tax	(20.1)	31.3	(24.7)	19.0
Comprehensive income (loss)	$ (61.8)	$ (90.9)	$ (61.6)	$ (357.4)