Equity, Accumulated Other Comprehensive Income, Net of Tax (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) Dividend	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Number of quarterly cash dividends declared | Dividend									4
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Beginning Balance				$ (13.8)				$ 64.6	$ (13.8)	$ 64.6
Other comprehensive gain (loss) before reclassifications									(14.5)	30.4
Amount reclassified from accumulated other comprehensive income									9.1	(108.8)
Other comprehensive gain (loss), net									(5.4)	(78.4)	$ 59.9
Ending Balance	$ (19.2)				$ (13.8)				(19.2)	(13.8)	64.6
Other expense	(18.5)	$ (8.4)	$ (17.1)	(15.8)	7.4	$ (6.8)	$ 178.6	154.2	(59.8)	333.4	(40.4)
Research and development expense	247.2	247.0	251.6	248.7	233.5	253.2	255.5	264.0	994.5	1,006.2	1,043.2
Selling and marketing expense	255.9	235.3	232.4	220.2	243.0	249.2	258.0	273.4	943.8	1,023.6	1,075.9
General and administrative expense	60.3	57.1	56.3	55.2	40.6	55.0	60.6	74.9	228.9	231.1	217.3
Cost of revenues	477.2	$ 451.2	$ 440.7	410.1	426.5	$ 411.1	$ 481.3	450.0	1,779.2	1,768.9	1,727.7
Unrealized Gains (Losses) on Available-for- Sale Securities [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Beginning Balance				8.4				66.2	8.4	66.2
Other comprehensive gain (loss) before reclassifications									9.1	48.7
Amount reclassified from accumulated other comprehensive income									0.5	(106.5)
Other comprehensive gain (loss), net									8.6	(57.8)
Ending Balance	17.0				8.4				17.0	8.4	66.2
Other expense									0.5	104.3
Research and development expense										1.4
Selling and marketing expense										0.3
General and administrative expense										0.7
Cost of revenues										0.1
Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Beginning Balance				(4.2)				2.2	(4.2)	2.2
Other comprehensive gain (loss) before reclassifications									(6.7)	(4.1)
Amount reclassified from accumulated other comprehensive income									(9.6)	(2.3)
Other comprehensive gain (loss), net									2.9	(6.4)
Ending Balance	(1.3)				(4.2)				(1.3)	(4.2)	2.2
Research and development expense									0.2
Selling and marketing expense									6.0
General and administrative expense									0.5
Cost of revenues									2.9
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Beginning Balance				$ (18.0)				$ (3.8)	(18.0)	(3.8)
Other comprehensive gain (loss) before reclassifications									(16.9)	(14.2)
Amount reclassified from accumulated other comprehensive income									0.0	0.0
Other comprehensive gain (loss), net									(16.9)	(14.2)
Ending Balance	$ (34.9)				$ (18.0)				$ (34.9)	$ (18.0)	$ (3.8)