Segment Information - Additional Significant Financial Information by Segment (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Segment Reporting [Line Items]
Assets	$ 15,400.5	$ 15,266.6
Corporate & Other
Segment Reporting [Line Items]
Assets	381.6	308.8
Operating Segments \| Property & Casualty
Segment Reporting [Line Items]
Assets	1,338.4	1,372.1
Operating Segments \| Life & Retirement
Segment Reporting [Line Items]
Assets	12,437.0	12,204.5
Operating Segments \| Supplemental & Group Benefits
Segment Reporting [Line Items]
Assets	1,278.9	1,401.7
Intersegment eliminations
Segment Reporting [Line Items]
Assets	$ (35.4)	$ (20.5)

Amount of asset recognized for present right to economic benefit.

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+ Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details