Goodwill and Acquired Client Relationships - Schedule of Changes in, and the Components of, Acquired Client Relationships (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Book Value
Net book value balance at the beginning of the period	$ 1,686.4
Intangible amortization and impairments	(110.2)	$ (115.4)	$ (122.2)
Net book value balance at the end of the period	1,497.4	1,686.4
Customer Relationships
Definite-lived
Gross book value, balance at the beginning of the period	1,301.8	1,255.1
Accumulated amortization, balance at the beginning of the period	(680.4)	(565.0)
Net book value, balance at the beginning of the period	621.4	690.1
New Investments	0.0	52.5
Intangible amortization and impairments	(107.7)	(115.4)
Foreign currency translation	(11.8)	(5.8)
Gross book value, balance at the end of the period	1,290.0	1,301.8	1,255.1
Accumulated amortization, balance at the end of the period	(788.1)	(680.4)	(565.0)
Net book value, balance at the end of the period	501.9	621.4	690.1
Indefinite-lived
Net book value, balance at the beginning of the period	1,065.0	1,088.3
New investments	0.0	0.0
Impairment	(2.5)	0.0
Foreign currency translation	(67.0)	(23.3)
Net book value, balance at the end of the period	995.5	1,065.0	1,088.3
Net Book Value
Net book value balance at the beginning of the period	1,686.4	1,778.4
New investments	0.0	52.5
Intangible amortization and impairments	(110.2)	(115.4)
Foreign currency translation	(78.8)	(29.1)
Net book value balance at the end of the period	$ 1,497.4	$ 1,686.4	$ 1,778.4