Equity, Components of Accumulated Other Comprehensive (Loss) Income, Net of Tax (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive (Loss) Income, Net of Tax [Roll Forward]
Balance as of December 31, 2014			$ (13.8)
Other comprehensive gain (loss) before reclassifications			0.1
Amount reclassified from accumulated other comprehensive income			6.4
Other comprehensive income (loss), net of tax	$ 21.9	$ 11.2	6.5	$ (51.5)
Balance as of June 30, 2015	(7.3)		(7.3)
Cost of revenues	440.7	481.3	850.8	931.3
Sales and marketing	232.4	258.0	452.6	531.4
General and administrative	56.3	$ 60.6	111.5	$ 135.5
Unrealized Gains (Losses) on Available-for- Sale Securities
Accumulated Other Comprehensive (Loss) Income, Net of Tax [Roll Forward]
Balance as of December 31, 2014			8.4
Other comprehensive gain (loss) before reclassifications			8.2
Amount reclassified from accumulated other comprehensive income			(0.5)
Other comprehensive income (loss), net of tax			7.7
Balance as of June 30, 2015	16.1		16.1
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive (Loss) Income, Net of Tax [Roll Forward]
Balance as of December 31, 2014			(4.2)
Other comprehensive gain (loss) before reclassifications			(4.0)
Amount reclassified from accumulated other comprehensive income			6.9
Other comprehensive income (loss), net of tax			2.9
Balance as of June 30, 2015	(1.3)		(1.3)
Cost of revenues			2.1
Sales and marketing			4.4
General and administrative			0.4
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive (Loss) Income, Net of Tax [Roll Forward]
Balance as of December 31, 2014			(18.0)
Other comprehensive gain (loss) before reclassifications			(4.1)
Amount reclassified from accumulated other comprehensive income			0.0
Other comprehensive income (loss), net of tax			(4.1)
Balance as of June 30, 2015	$ (22.1)		$ (22.1)