Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenue		$ 467.4	$ 401.5	$ 922.4	$ 787.1
Cost of revenue	[1]	102.5	102.9	205.6	201.3
Gross profit		364.9	298.6	716.8	585.8
Operating expenses
Research and development	[1]	185.8	162.4	367.6	312.4
Sales and marketing	[1]	102.8	107.3	207.1	208.8
General and administrative	[1]	63.5	62.9	102.5	119.9
Total operating expenses	[1]	352.1	332.6	677.2	641.1
Income (loss) from operations		12.8	(34.0)	39.6	(55.3)
Interest income, net		0.1	3.2	2.5	6.9
Other income, net		9.0	10.0	19.6	14.2
Income (loss) before income taxes		21.9	(20.8)	61.7	(34.2)
Benefit from (provision for) income taxes		(4.4)	(0.6)	(4.9)	5.1
Net income (loss)		$ 17.5	$ (21.4)	$ 56.8	$ (29.1)
Basic net income (loss) per share (in dollars per share)		$ 0.04	$ (0.05)	$ 0.14	$ (0.07)
Diluted net income (loss) per share (in dollars per share)		$ 0.04	$ (0.05)	$ 0.14	$ (0.07)
Weighted-average shares used in computed net income (loss) per share attributable to common shareholders, basic (in shares)		414.1	412.4	415.7	411.5
Weighted-average shares used in computed net income (loss) per share attributable to common shareholders, diluted (in shares)		420.5	412.4	419.7	411.5

[1] Includes stock-based compensation as follows (in millions):
  Three Months Ended
June 30,   Six Months Ended
June 30,   2020   2019   2020   2019                 Cost of revenue $ 4.5
  $ 4.7
  $ 8.0
  $ 7.7
Research and development 47.0
  37.7
  84.2
  68.2
Sales and marketing 9.5
  8.8
  16.2
  15.9
General and administrative⁽²⁾ 15.6
  16.9
  8.0
  31.9