Income taxes (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 29, 2014	Jun. 30, 2013	Jun. 29, 2014	Jun. 30, 2013	Dec. 29, 2013
Income Taxes (Textual) [Abstract]
Unrecognized tax benefits that, if recognized, would impact effective tax rate	$ 45.0		$ 45.0		$ 46.5
Net benefit from the reversal of interest and penalty expense	1.2	4.6	2.5	17.4
Accrued interest and penalties payable related to unrecognized tax benefits	9.0		9.0		11.5
Estimated decrease in gross unrecognized tax positions within the next 12 months, maximum	$ 8.2		$ 8.2
Federal [Member]
Income Tax Examination [Line Items]
Tax years subject to examination			2010 through 2012 tax years remain subject to IRS examination
State [Member]
Income Tax Examination [Line Items]
Tax years subject to examination			The 2009 through 2012 tax years generally remain subject to examination by state authorities
UNITED KINGDOM
Income Tax Examination [Line Items]
Tax years subject to examination			the 2012 tax year is subject to examination in the U.K