Future minimum lease payments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating Leases, Rent Expense	$ 357.7us-gaap_LeaseAndRentalExpense	$ 366.1us-gaap_LeaseAndRentalExpense	$ 358.5us-gaap_LeaseAndRentalExpense
Rent Obligations, due 2015	328.4
Rent Obligations, due 2016	288.9
Rent Obligations, due 2017	248.3
Rent Obligations, due 2018	222.3
Rent Obligations, due 2019	198.9
Rent Obligations, due thereafter	845.1
Total Rent Obligations	2,131.9
Sublease Rental Income, due 2015	(8.4)
Sublease Rental Income, due 2016	(2.8)
Sublease Rental Income, due 2017	(1.1)
Sublease Rental Income, due 2018	(0.1)
Sublease Rental Income, due 2019	0
Sublease Rental Income, due thereafter	0
Total Sublease Rental Income	(12.4)
Net Rent, due 2015	320.0
Net Rent, due 2016	286.1
Net Rent, due 2017	247.2
Net Rent, due 2018	222.2
Net Rent, due 2019	198.9
Net Rent, due thereafter	845.1
Total Net Rent	2,119.5
Operating Leases, Rent Expense, Sublease Rentals	6.1	16.1	17.5
Operating Leases, Rent Expense, Net	$ 351.6us-gaap_OperatingLeasesRentExpenseNet	$ 350.0us-gaap_OperatingLeasesRentExpenseNet	$ 341.0us-gaap_OperatingLeasesRentExpenseNet

Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, Current

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Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, Due in Five Years

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Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, Due in Four Years

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Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, Due in Three Years

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Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, Due in Two Years

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Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, Due Thereafter

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Operating Leases, Future Minimum Payments Due, Gross Rent

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Operating Leases, Future Minimum Payments Due, Gross Rent, Current

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Operating Leases, Future Minimum Payments, Gross Rent, Due in Five Years

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Operating Leases, Future Minimum Payments, Gross Rent, Due in Four Years

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Operating Leases, Future Minimum Payments, Gross Rent, Due in Three Years

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Operating Leases, Future Minimum Payments, Gross Rent, Due in Two Years

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Operating Leases, Future Minimum Payments, Gross Rent, Due Thereafter

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Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

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No definition available.

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Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 10

-Section 55

-Paragraph 40

-Subparagraph (Note 3)

-URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Contractually required future rental payments receivable on noncancelable subleasing arrangements.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41499-112717

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- Definition

The total amount of sublease rental income recognized during the period that reduces the entity's rent expense incurred under operating leases.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 10

-Section 55

-Paragraph 40

-Subparagraph (Note 3)

-URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697

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