Equity, Components of Accumulated Other Comprehensive (Loss) Income, Net of Tax (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive (Loss) Income, Net of Tax [Roll Forward]
Balance as of December 31, 2015	$ (19.2)
Other comprehensive gain before reclassifications	10.5
Amount reclassified from accumulated other comprehensive income	1.2
Other comprehensive income (loss), net of tax	11.7	$ (15.4)
Balance as of March 31, 2016	(7.5)
Cost of revenues	407.0	410.1
Sales and marketing	231.8	220.2
General and administrative	59.4	55.2
Research and development expense	251.0	248.7
Other expense, net	(22.2)	$ (15.8)
Unrealized Gains (Losses) on Available-for- Sale Securities
Accumulated Other Comprehensive (Loss) Income, Net of Tax [Roll Forward]
Balance as of December 31, 2015	17.0
Other comprehensive gain before reclassifications	4.3
Amount reclassified from accumulated other comprehensive income	0.1
Other comprehensive income (loss), net of tax	4.4
Balance as of March 31, 2016	21.4
Other expense, net	0.1
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive (Loss) Income, Net of Tax [Roll Forward]
Balance as of December 31, 2015	(1.3)
Other comprehensive gain before reclassifications	2.5
Amount reclassified from accumulated other comprehensive income	1.1
Other comprehensive income (loss), net of tax	3.6
Balance as of March 31, 2016	2.3
Cost of revenues	0.3
Sales and marketing	0.3
General and administrative	0.1
Research and development expense	0.4
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive (Loss) Income, Net of Tax [Roll Forward]
Balance as of December 31, 2015	(34.9)
Other comprehensive gain before reclassifications	3.7
Amount reclassified from accumulated other comprehensive income	0.0
Other comprehensive income (loss), net of tax	3.7
Balance as of March 31, 2016	$ (31.2)