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Goodwill and Acquired Client Relationships - Schedule of Changes in Acquired Client Relationships (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Book Value
Beginning balance, net book value		$ 1,309.9
Intangible amortization and impairments		(144.5)	$ (114.8)	$ (86.4)
Ending balance, net book value		1,182.0	1,309.9
Acquired Client Relationships (Net)
Definite-lived
Beginning balance, gross book value		1,292.5	1,295.5
Beginning balance, accumulated amortization		(988.9)	(874.5)
Beginning balance, net book value		303.6	421.0
Intangible amortization and impairments		(93.4)	(114.4)
Foreign currency translation		(0.4)	(3.0)
Transfer and other, gross book value	[1]	(36.1)
Transfer and other, accumulated amortization	[1]	36.1
Ending balance, gross book value		1,256.0	1,292.5	1,295.5
Ending balance, accumulated amortization		(1,046.2)	(988.9)	(874.5)
Ending balance, net book value		209.8	303.6	421.0
Indefinite-lived
Beginning balance, net book value		1,006.3	1,028.7
Intangible amortization and impairments		(51.1)	(0.4)
Foreign currency translation		17.0	(22.0)
Transfers(1)	[1]	0.0
Ending balance, net book value		972.2	1,006.3	1,028.7
Net Book Value
Beginning balance, net book value		1,309.9	1,449.7
Intangible amortization and impairments		(144.5)	(114.8)
Transfers(1)	[1]	0.0
Foreign currency translation		16.6	(25.0)
Transfers(1)	[1]	0.0
Ending balance, net book value		$ 1,182.0	$ 1,309.9	$ 1,449.7
[1] Transfers includes acquired client relationships at Affiliates that were deconsolidated during the period.

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