Segment Information (Identifiable Assets by Business Segment) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total assets	$ 13,443.7	$ 12,490.5
Identifiable assets	110.2	102.8
Assets of Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Identifiable assets	110.2	102.8
Property and Casualty [Member]
Segment Reporting Information [Line Items]
Total assets	$ 13,333.5	$ 12,387.7