Operating leases (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Leases, Annual minimum lease payments due [Abstract]
2013	$ 32.2
2014	22.5
2015	13.1
2016	9.1
2017	5.1
Thereafter	36.0
Rent expense
Rent expense	$ 42.9	$ 40.7	$ 38.7