Income taxes - Income and Taxes from Cont. Operations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income (loss) from continuing operations before income taxes [Abstract]
U.S.	$ (27.0)	$ (2.0)	$ 37.0
Foreign	183.4	141.6	129.3
Income from continuing operations before tax	156.4	139.6	166.3
Income tax expense (benefit) from continuing operations [Abstract]
U.S. federal - Current	3.0	4.3	(29.1)
State - Current	(0.1)	0.2	(0.8)
Foreign - Current	87.9	64.9	59.8
Current tax expense	90.8	69.4	29.9
U.S. federal - Deferred	(21.3)	(7.8)	(72.3)
State - Deferred	(1.0)	0	(8.1)
Foreign - Deferred	(9.1)	5.5	(10.6)
Deferred income taxes	(31.4)	(2.3)	(91.0)
Provision for income taxes	59.4	67.1	(61.1)
Comprehensive provision (benefit) for income taxes allocation [Abstract]
Continuing operations	59.4	67.1	(61.1)
Discontinued operations	0.7	(3.4)	2.3
Other comprehensive income (loss)	74.4	16.1	(10.6)
Shareholders' equity	(1.1)	(0.7)	(0.1)
Comprehensive provision (benefit) for income taxes	$ (15.4)	$ 46.9	$ (48.3)