Business Combinations, Textuals (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			0 Months Ended
	Dec. 31, 2014 Acquisition	Dec. 31, 2013 Acquisition	Dec. 31, 2012 Acquisition	Jan. 07, 2014	Dec. 14, 2012	Feb. 13, 2012	Mar. 08, 2012	Dec. 13, 2012
Business Acquisition [Line Items]
Length of time subsequent to acquisition date may result in changes of additional information	12 months
Number of Businesses Acquired	1	1	3
Goodwill	$ 2,981.5	$ 4,057.7	$ 4,057.8
Privately-held investments	47.5
2014 Acquisitions [Member]
Business Acquisition [Line Items]
Consideration Transferred	28.7
Net tangible assets acquired	0
Intangible assets acquired	17.8
Goodwill	13.6
2013 Acquisitions [Member]
Business Acquisition [Line Items]
Consideration Transferred		10.0
Net tangible assets acquired		0.1
Intangible assets acquired		9.9
Acquired intangible asset, weighted average estimated useful life (in years)		5 years
Goodwill		0
2012 Acquisitions [Member]
Business Acquisition [Line Items]
Consideration Transferred			187.3
Net tangible assets acquired			3.5
Intangible assets acquired			54.1
Goodwill			129.7
WANDL, Inc, [Member]
Business Acquisition [Line Items]
Intangible assets acquired	17.8
Acquired intangible asset, weighted average estimated useful life (in years)	7 years
WANDL, Inc, [Member] | 2014 Acquisitions [Member]
Business Acquisition [Line Items]
Consideration Transferred				28.7
Percentage of interests acquired				100.00%
Share-based awards assumed, fair value				34.9
Business Acquisition Acquired Entity Contrail [Member] | 2012 Acquisitions [Member]
Business Acquisition [Line Items]
Consideration Transferred					91.7
Intangible assets acquired			17.4		17.4
Percentage of interests acquired, original					12.00%
Percentage of interest acquired, subsequent					100.00%
Net tangible assets acquired					3.6
Cash and cash equivalents acquired					8.6
Goodwill					70.7
Privately-held investments								3.0
Fair value of equity interest, original					17.7
Remeasurement gain			14.7
Business Acquisition Acquired Entity Mykonos [Member] | 2012 Acquisitions [Member]
Business Acquisition [Line Items]
Percentage of interests acquired						100.00%
Intangible assets acquired			24.3			24.3
Acquired intangible asset, weighted average estimated useful life (in years)			6 years
Net tangible assets acquired						0.2
Goodwill						58.5
Cash paid for business acquisition						82.6
Business Acquisition Acquired Entity BitGravity [Member] | 2012 Acquisitions [Member]
Business Acquisition [Line Items]
Intangible assets acquired			12.4				12.4
Acquired intangible asset, weighted average estimated useful life (in years)			3 years
Net tangible assets acquired							0.1
Goodwill							0.5
Cash paid for business acquisition							$ 13.0