Segment information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Segment Revenue and Operating Profit [Line Items]
Revenues	$ 979.0	$ 995.8	$ 2,912.9	$ 2,888.4
Operating profit	37.1	62.5	106.0	119.9
Capital expenditures			120.6	118.7
Depreciation and amortization			126.0	120.5
Total assets	2,563.9		2,563.9		2,406.2
International [Member]
Segment Revenue and Operating Profit [Line Items]
Revenues	744.4	751.3	2,204.3	2,158.1
Operating profit	50.8	61.4	148.1	132.8
North America [Member]
Segment Revenue and Operating Profit [Line Items]
Revenues	234.6	244.5	708.6	730.3
Operating profit	8.3	8.7	25.5	25.9
Segment operating profit [Member]
Segment Revenue and Operating Profit [Line Items]
Operating profit	59.1	70.1	173.6	158.7
Non Segment [Member]
Segment Revenue and Operating Profit [Line Items]
Operating profit	$ (22.0)	$ (7.6)	$ (67.6)	$ (38.8)