Income taxes - Income and Taxes from Cont. Operations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income (loss) from continuing operations before income taxes [Abstract]
U.S.	$ (19.6)	$ (16.0)	$ (7.1)
Foreign	174.1	200.4	177.0
Income from continuing operations before tax	154.5	184.4	169.9
Income tax expense (benefit) from continuing operations [Abstract]
U.S. federal - Current	(0.1)	2.9	4.3
State - Current	(0.3)	(0.1)	0.2
Foreign - Current	71.2	92.3	69.6
Current tax expense	70.8	95.1	74.1
U.S. federal - Deferred	(29.9)	(21.3)	(7.8)
State - Deferred	(1.4)	(0.9)	0
Foreign - Deferred	(12.6)	(9.0)	6.3
Deferred income taxes	(43.9)	(31.2)	(1.5)
Provision (benefit) for income taxes	26.9	63.9	72.6
Comprehensive provision (benefit) for income taxes allocation [Abstract]
Continuing operations	26.9	63.9	72.6
Discontinued operations	(0.9)	(3.8)	(8.9)
Other comprehensive income (loss)	(9.3)	74.4	16.1
Shareholders' equity	2.7	(1.1)	(0.7)
Comprehensive provision (benefit) for income taxes	$ 38.0	$ (15.4)	$ 46.9