Operating Segment and Related Information - Long-term investments, Property and Equipment and Assets (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Revenues from External Customers and Long-Lived Assets [Line Items]
Investments	$ 53.1	$ 55.4
Total Assets	6,935.9	6,742.8
Operating Segments | Infrastructure
Revenues from External Customers and Long-Lived Assets [Line Items]
Investments	0.9	0.9
Total Assets	858.9	494.8
Operating Segments | Life Sciences
Revenues from External Customers and Long-Lived Assets [Line Items]
Investments	15.1	18.4
Total Assets	20.4	21.4
Operating Segments | Spectrum
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Assets	206.0	213.6
Operating Segments | Insurance
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Assets	5,849.0	5,854.0
Operating Segments | Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Investments	37.1	36.1
Total Assets	40.8	167.3
Non-operating Corporate
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Assets	4.2	30.1
Eliminations
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Assets	$ (43.4)	$ (38.4)