Income taxes - Income and Taxes from Cont. Operations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income (loss) from continuing operations before income taxes [Abstract]
U.S.	$ (51.8)	$ (19.6)	$ (16.0)
Foreign	200.0	178.7	204.3
Income from continuing operations before tax	148.2	159.1	188.3
Income tax expense (benefit) from continuing operations [Abstract]
U.S. federal - Current	0.5	(0.1)	2.9
State - Current	1.5	(0.3)	(0.1)
Foreign - Current	84.6	70.9	91.9
Current tax expense	86.6	70.5	94.7
U.S. federal - Deferred	(20.6)	(29.9)	(21.3)
State - Deferred	(1.9)	(1.4)	(0.9)
Foreign - Deferred	(12.1)	(12.1)	(8.5)
Deferred income taxes	(34.6)	(43.4)	(30.7)
Provision (benefit) for income taxes	52.0	27.1	64.0
Comprehensive provision (benefit) for income taxes allocation [Abstract]
Provision Continuing Operations	52.0	27.1	64.0
Discontinued operations	4.7	(1.0)	(3.9)
Other comprehensive income (loss)	(141.0)	(9.3)	74.4
Shareholders' equity	2.8	2.7	(1.1)
Comprehensive provision (benefit) for income taxes	$ 200.5	$ 38.1	$ (15.4)