Segment information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Segment Revenue and Operating Profit [Line Items]
Revenues	$ 967.1	$ 979.3	$ 1,933.9	$ 1,892.6
Operating profit	26.5	20.4	68.9	57.4
Capital expenditures			73.0	71.6
Depreciation and amortization			83.9	80.0
Total assets	2,460.2		2,460.2		2,406.2
International [Member]
Segment Revenue and Operating Profit [Line Items]
Revenues	729.5	732.5	1,459.9	1,406.8
Operating profit	36.4	26.2	97.3	71.4
North America [Member]
Segment Revenue and Operating Profit [Line Items]
Revenues	237.6	246.8	474.0	485.8
Operating profit	11.4	10.4	17.2	17.2
Segment operating profit [Member]
Segment Revenue and Operating Profit [Line Items]
Operating profit	47.8	36.6	114.5	88.6
Non Segment [Member]
Segment Revenue and Operating Profit [Line Items]
Operating profit	$ (21.3)	$ (16.2)	$ (45.6)	$ (31.2)