Goodwill and Other Intangible Assets - Intangible Assets by Asset Type (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets [Line Items]
Gross Carrying Amount	$ 2,694.5	$ 2,655.3
Accumulated Amortization	(1,797.5)	(1,599.7)
Net Carrying Amount	897.0	1,055.6
Customer relationships and contracts
Intangible Assets [Line Items]
Gross Carrying Amount	2,106.8	2,084.6
Accumulated Amortization	(1,490.8)	(1,322.7)
Net Carrying Amount	616.0	761.9
Trade name
Intangible Assets [Line Items]
Gross Carrying Amount	422.2	422.1
Accumulated Amortization	(216.3)	(195.2)
Net Carrying Amount	205.9	226.9
Internally developed software
Intangible Assets [Line Items]
Gross Carrying Amount	162.6	142.6
Accumulated Amortization	(89.6)	(77.7)
Net Carrying Amount	73.0	64.9
Other
Intangible Assets [Line Items]
Gross Carrying Amount	2.9	6.0
Accumulated Amortization	(0.8)	(4.1)
Net Carrying Amount	$ 2.1	$ 1.9