Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Net unrealized investment gains (losses) on fixed maturity securities, net of tax
Beginning balance			$ 1,175.3
Other comprehensive income (loss) before reclassifications	$ 7.9	$ (23.8)	28.8	$ 26.3
Amounts reclassified from AOCI	1.7	11.6	2.5	13.5
Other comprehensive income	9.6	(12.2)	31.3	39.8
Ending balance	1,208.8	1,101.9	1,208.8	1,101.9
Pretax reclassification amounts from AOCI, tax	(0.5)	(3.1)	(0.7)	(3.6)
Total
Net unrealized investment gains (losses) on fixed maturity securities, net of tax
Beginning balance	(292.3)	(347.4)	(314.0)	(399.4)
Ending balance	(282.7)	(359.6)	(282.7)	(359.6)
Net Unrealized Investment Gains (Losses) on Fixed Maturity Securities
Net unrealized investment gains (losses) on fixed maturity securities, net of tax
Beginning balance	(348.0)	(356.4)	(328.3)	(449.6)
Other comprehensive income (loss) before reclassifications	(24.1)	(48.9)	(44.6)	42.4
Amounts reclassified from AOCI	1.7	11.6	2.5	13.5
Other comprehensive income	(22.4)	(37.3)	(42.1)	55.9
Ending balance	(370.4)	(393.7)	(370.4)	(393.7)
Pretax reclassification amounts from accumulated other comprehensive income (loss)	(2.2)	(14.6)	(3.2)	(17.0)
Net Reserve Remeasurements Attributable to Discount Rates
Net unrealized investment gains (losses) on fixed maturity securities, net of tax
Beginning balance	63.3	17.8	21.9	59.0
Other comprehensive income (loss) before reclassifications	32.0	25.1	73.4	(16.1)
Amounts reclassified from AOCI	0.0	0.0	0.0	0.0
Other comprehensive income	32.0	25.1	73.4	(16.1)
Ending balance	95.3	42.9	95.3	42.9
Net Funded Status of Benefit Plans
Net unrealized investment gains (losses) on fixed maturity securities, net of tax
Beginning balance	(7.6)	(8.8)	(7.6)	(8.8)
Other comprehensive income (loss) before reclassifications	0.0	0.0	0.0	0.0
Amounts reclassified from AOCI	0.0	0.0	0.0	0.0
Other comprehensive income	0.0	0.0	0.0	0.0
Ending balance	$ (7.6)	$ (8.8)	$ (7.6)	$ (8.8)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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