Summary of Significant Accounting Policies (Details) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
Operating Lease, Right-of-Use Asset	$ 1,574.4	$ 0.0			$ 1,421.1
Operating Lease, Liability	1,696.8				$ 1,544.4
Revenue, remaining performance obligation, amount	$ 704.0
Retirement of treasury stock, amount		(0.0)	$ (0.0)
ERP Systems, Useful Life	P10Y
Minimum Remaining Lease Term	1 year
Maximum Remaining Lease Term	20 years
Leasehold Improvements, Useful Life	the shorter of the useful life or the remaining lease term
Number of Reporting Units for Purposes of Annual Goodwill Impairment Test	12
Foreign Currency Transaction pre-tax Gain (Loss)	$ 5.3	$ (5.6)	$ (1.9)
Minimum
Furniture and Equipment, Useful Life	3 years
Buildings, Useful Life	10 years
Other Internal Use Software, Useful Life	P3Y
Identifiable Intangible Assets, Useful Life	7 years
Maximum
Furniture and Equipment, Useful Life	7 years
Buildings, Useful Life	35 years
Other Internal Use Software, Useful Life	P7Y
Identifiable Intangible Assets, Useful Life	15 years
Common Stock [Member]
Retirement of treasury stock, shares | shares		8.1	13.4
Retirement of treasury stock, amount		$ (0.8)	$ (1.3)
Treasury Stock [Member]
Retirement of treasury stock, amount		(176.1)	(304.4)
Additional Paid-in Capital [Member]
Retirement of treasury stock, amount		$ (175.3)	$ (303.1)