Business and Geographic Segments - Revenue and Long-Lived Assets by Geographic Segment (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Geographic Segments
Revenue	$ 565.8	$ 415.6	$ 416.9	$ 388.1	$ 401.9	$ 234.4	$ 235.0	$ 219.6	$ 246.8	$ 224.6	$ 226.0	$ 231.2	$ 1,786.4	$ 1,090.9	$ 928.6
Long-lived assets (excluding identifiable intangibles):	1,012.8				773.1								1,012.8	773.1
United States
Geographic Segments
Revenue													1,070.1	559.8	445.2
Long-lived assets (excluding identifiable intangibles):	771.1				580.3								771.1	580.3
International
Geographic Segments
Revenue													716.3	531.1	483.4
Long-lived assets (excluding identifiable intangibles):	242.2				192.8								242.2	192.8
North America, other than United States
Geographic Segments
Revenue													131.0	74.2	66.1
Long-lived assets (excluding identifiable intangibles):	59.9				47.5								59.9	47.5
United Kingdom
Geographic Segments
Revenue													162.5	157.5	163.7
Long-lived assets (excluding identifiable intangibles):	96.6				85.2								96.6	85.2
Europe, other than the United Kingdom
Geographic Segments
Revenue													283.6	213.2	187.6
Long-lived assets (excluding identifiable intangibles):	34.2				19.6								34.2	19.6
Other
Geographic Segments
Revenue													139.2	86.2	66.0
Long-lived assets (excluding identifiable intangibles):	$ 51.0				$ 40.5								$ 51.0	$ 40.5