Geographic Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 5,147.1	$ 4,644.6	$ 4,050.4
Long-lived assets	402.6	350.8	349.6
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	2,546.4	2,328.6	2,057.1
Long-lived assets	279.2	225.8	228.7
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	1,374.5	1,342.1	1,169.9
Long-lived assets	91.6	91.9	82.2
Continental Europe/Ireland
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	604.7	411.0	299.5
Long-lived assets	6.6	8.1	8.5
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	387.7	365.0	333.2
Long-lived assets	9.9	9.5	9.4
Asia
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	233.8	197.9	190.7
Long-lived assets	15.3	15.5	20.8
External Customers
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	5,147.1	4,644.6	4,050.4
External Customers | United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	2,534.9	2,332.2	2,063.6
External Customers | United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	1,286.7	1,294.0	1,137.9
External Customers | Continental Europe/Ireland
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	810.2	541.9	397.2
External Customers | Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	396.6	374.8	346.4
External Customers | Asia
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	118.7	101.7	105.3
Inter-company Customers
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	0	0	0
Inter-company Customers | United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	11.5	(3.6)	(6.5)
Inter-company Customers | United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	87.8	48.1	32.0
Inter-company Customers | Continental Europe/Ireland
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	(205.5)	(130.9)	(97.7)
Inter-company Customers | Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	(8.9)	(9.8)	(13.2)
Inter-company Customers | Asia
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 115.1	$ 96.2	$ 85.4