Accumulated Other Comprehensive Income (Loss) - Schedule of Amounts Reclassified from Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Unrealized gains and losses on securities:
Net investment and other (gains) losses	$ (9.7)	$ (6.2)	$ (6.2)
Income tax provision (benefit)	8.3	1.6
Net income (loss)	30.2	25.6
Reclassification out of Accumulated Other Comprehensive Income
Unrealized gains and losses on securities:
Net income (loss)	1.0	(5.2)
Unrealized Gains and Losses on Securities \| Reclassification out of Accumulated Other Comprehensive Income
Unrealized gains and losses on securities:
Net investment and other (gains) losses	1.3	(6.5)
Income tax provision (benefit)	$ (0.3)	$ 1.3

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details