Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue		$ 487.4	$ 428.2	$ 1,409.8	$ 1,215.3
Cost of revenue	[1]	103.2	104.8	308.8	306.1
Gross profit		384.2	323.4	1,101.0	909.2
Operating expenses
Research and development	[1]	183.3	172.8	550.9	485.2
Sales and marketing	[1]	105.8	108.2	312.9	317.0
General and administrative	[1]	65.1	61.0	167.6	180.9
Total operating expenses	[1]	354.2	342.0	1,031.4	983.1
Income (loss) from operations		30.0	(18.6)	69.6	(73.9)
Interest income, net		0.1	3.0	2.6	9.9
Other income, net		3.5	0.2	23.1	14.4
Income (loss) before income taxes		33.6	(15.4)	95.3	(49.6)
Benefit from (provision for) income taxes		(0.9)	(1.6)	(5.8)	3.5
Net income (loss)		$ 32.7	$ (17.0)	$ 89.5	$ (46.1)
Basic net income (loss) per share (in dollars per share)		$ 0.08	$ (0.04)	$ 0.22	$ (0.11)
Diluted net income (loss) per share (in dollars per share)		$ 0.08	$ (0.04)	$ 0.21	$ (0.11)
Weighted-average shares used in computed net income (loss) per share attributable to common shareholders, basic (in shares)		414.2	414.4	415.2	412.4
Weighted-average shares used in computed net income (loss) per share attributable to common shareholders, diluted (in shares)		419.9	414.4	419.9	412.4

[1] Includes stock-based compensation as follows (in millions): Three Months Ended
September 30,Nine Months Ended
September 30,2020201920202019Cost of revenue$4.6 $4.1 $12.6 $11.8 Research and development46.9 38.9 131.1 107.1 Sales and marketing8.9 7.7 25.1 23.6  General and administrative(2) 15.3 17.5 23.3 49.4