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Segment Information (Identifiable Assets by Business Segment) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Identifiable assets	$ 15,367.0	$ 14,612.6
Identifiable assets	89.1	86.6
Property and Casualty [Member]
Segment Reporting Information [Line Items]
Identifiable assets	15,277.9	14,526.0
Assets of Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Identifiable assets	$ 89.1	$ 86.6

X

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