Segment information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Segment Revenue and Operating Profit [Line Items]
Revenues	$ 966.8	$ 913.3
Operating profit	42.4	37.0
Capital expenditures	34.3	29.4
Depreciation and amortization	42.2	38.8
Total assets	2,514.8		2,406.2
International [Member]
Segment Revenue and Operating Profit [Line Items]
Revenues	730.4	674.3
Operating profit	60.9	45.2
North America [Member]
Segment Revenue and Operating Profit [Line Items]
Revenues	236.4	239.0
Operating profit	5.8	6.8
Segment operating profit [Member]
Segment Revenue and Operating Profit [Line Items]
Operating profit	66.7	52.0
Non Segment [Member]
Segment Revenue and Operating Profit [Line Items]
Operating profit	$ (24.3)	$ (15.0)