Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 1,224.4	$ 596.2
Accumulated amortization	(490.6)	(446.2)
Net carrying amount	733.8	150.0
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,205.2	587.1
Accumulated amortization	(484.6)	(441.4)
Net carrying amount	720.6	145.7
Other
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	19.2	9.1
Accumulated amortization	(6.0)	(4.8)
Net carrying amount	$ 13.2	$ 4.3