Segment Information (Identifiable Assets by Business Segment) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Segment Reporting Information [Line Items]
Identifiable assets	$ 15,470.3	$ 15,274.5
Identifiable assets	85.7	85.7
Property and Casualty [Member]
Segment Reporting Information [Line Items]
Identifiable assets	15,384.6	15,188.8
Assets of Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Identifiable assets	$ 85.7	$ 85.7