Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets amortization	$ 3.9	$ 4.2	$ 8.2	$ 8.3
Goodwill	709.4		709.4		$ 707.2
Parilux Investment Technology, LLC
Acquired Finite-Lived Intangible Assets [Line Items]
Consideration transferred	17.6
Goodwill	4.2		4.2
Developed technology acquired	13.4		13.4
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets amortization	3.9	4.2	8.2	8.3
Estimated future amortization expense for 2021	6.6		6.6
Estimated future amortization expense for 2022	10.2		10.2
Estimated future amortization expense for 2023	9.9		9.9
Estimated future amortization expense for 2024	9.8		9.8
Estimated future amortization expense for 2025	9.2		9.2
Computer Software
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets amortization	$ 95.9	$ 91.1	$ 189.9	$ 182.7