Supplementary Data Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Furniture and equipment	$ 604.2	$ 585.1
Leasehold improvements	599.8	570.1
Internal use computer software	306.5	295.2
Land and buildings	73.1	78.7
Total property and equipment, gross	1,583.6	1,529.1
Less: accumulated depreciation	961.6	961.9
Total property and equipment, net	622.0	567.2
Depreciation and amortization expense for property and equipment	$ 138.3	$ 130.9	$ 133.7