Goodwill and Other Intangible Assets - Schedule of Goodwill by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Goodwill [Roll Forward]
Beginning balance	$ 4,342.7	$ 4,382.9
Acquisition activity	56.0
Sirius measurement period adjustment		(5.8)
Foreign currency translation	14.7	(34.4)
Ending balance	4,413.4	4,342.7
Corporate
Goodwill [Roll Forward]
Beginning balance	2,133.4	2,024.4
Acquisition activity	19.7
Sirius measurement period adjustment		109.0
Foreign currency translation	0.0	0.0
Ending balance	2,153.1	2,133.4
Accumulated impairment losses	1,571.0
Small Business
Goodwill [Roll Forward]
Beginning balance	230.2	266.1
Acquisition activity	0.0
Sirius measurement period adjustment		(35.9)
Foreign currency translation	0.0	0.0
Ending balance	230.2	230.2
Public
Goodwill [Roll Forward]
Beginning balance	1,658.8	1,737.7
Acquisition activity	36.3
Sirius measurement period adjustment		(78.9)
Foreign currency translation	0.0	0.0
Ending balance	1,695.1	1,658.8
Accumulated impairment losses	354.0
Other
Goodwill [Roll Forward]
Beginning balance	320.3	354.7
Acquisition activity	0.0
Sirius measurement period adjustment		0.0
Foreign currency translation	14.7	(34.4)
Ending balance	335.0	$ 320.3
Accumulated impairment losses	$ 28.0