Goodwill and Other Intangible Assets - Schedule of Goodwill by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Beginning balance	$ 2,553.0	$ 2,462.8
Foreign currency translation	9.9	11.7
Ending balance	2,595.9	2,553.0
Corporate
Goodwill [Roll Forward]
Beginning balance	1,090.6	1,074.1
Foreign currency translation	0.0	0.0
Ending balance	1,123.6	1,090.6
Accumulated impairment losses	1,571.0
Small Business
Goodwill [Roll Forward]
Beginning balance	185.9	185.9
Foreign currency translation	0.0	0.0
Ending balance	185.9	185.9
Public
Goodwill [Roll Forward]
Beginning balance	929.6	929.6
Foreign currency translation	0.0	0.0
Ending balance	929.6	929.6
Accumulated impairment losses	354.0
Other
Goodwill [Roll Forward]
Beginning balance	346.9	273.2
Foreign currency translation	9.9	11.7
Ending balance	356.8	346.9
Accumulated impairment losses	28.0
Scalar acquisition
Goodwill [Roll Forward]
Acquisition		62.0
Scalar acquisition | Corporate
Goodwill [Roll Forward]
Acquisition		0.0
Scalar acquisition | Small Business
Goodwill [Roll Forward]
Acquisition		0.0
Scalar acquisition | Public
Goodwill [Roll Forward]
Acquisition		0.0
Scalar acquisition | Other
Goodwill [Roll Forward]
Acquisition		62.0
Other acquisition
Goodwill [Roll Forward]
Acquisition		16.5
Other acquisition | Corporate
Goodwill [Roll Forward]
Acquisition		16.5
Other acquisition | Small Business
Goodwill [Roll Forward]
Acquisition		0.0
Other acquisition | Public
Goodwill [Roll Forward]
Acquisition		0.0
Other acquisition | Other
Goodwill [Roll Forward]
Acquisition		$ 0.0
IGNW, Inc.
Goodwill [Roll Forward]
Acquisition	33.0
IGNW, Inc. | Corporate
Goodwill [Roll Forward]
Acquisition	33.0
IGNW, Inc. | Small Business
Goodwill [Roll Forward]
Acquisition	0.0
IGNW, Inc. | Public
Goodwill [Roll Forward]
Acquisition	0.0
IGNW, Inc. | Other
Goodwill [Roll Forward]
Acquisition	$ 0.0