Segment Information (Identifiable Assets by Business Segment) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Identifiable assets	$ 13,997.2	$ 14,254.3
Identifiable assets	86.2	107.1
Property and Casualty [Member]
Segment Reporting Information [Line Items]
Identifiable assets	13,911.0	14,147.2
Assets of Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Identifiable assets	$ 86.2	$ 107.1