Derivative Financial Instruments Fair Value Hedges Carrying Amount of Hedged Assets and Liabilities and Cumulative Basis Adjustments (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Derivative Instruments and Hedging Activities Disclosures
Derivative, Notional Amount	$ 3,818.2	$ 3,751.4
Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures
Derivative, Notional Amount	3,498.9	3,445.5
Receive Fixed/Pay Fixed \| Designated as Hedging Instrument \| Fair Value Hedging
Derivative Instruments and Hedging Activities Disclosures
Hedged Asset, Fair Value Hedge	$ 695.0	$ 551.0
Hedged Asset, Statement of Financial Position [Extensible Enumeration]	Fixed Maturity Securities - at fair value (amortized cost of $34,747.2; $38,269.9; allowance for credit losses of $5.9; $2.8)	Fixed Maturity Securities - at fair value (amortized cost of $34,747.2; $38,269.9; allowance for credit losses of $5.9; $2.8)
Receive Fixed/Pay Fixed \| Designated as Hedging Instrument \| Fair Value Hedging \| Fixed Maturity Securities
Derivative Instruments and Hedging Activities Disclosures
Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease)	$ 24.7	$ (46.3)
Hedged asset, amortized cost	793.4	648.4
Interest Rate Swaps \| Designated as Hedging Instrument \| Fair Value Hedging
Derivative Instruments and Hedging Activities Disclosures
Derivative, Notional Amount	768.6	736.4
Interest Rate Swaps \| Receive Fixed/Pay Fixed \| Designated as Hedging Instrument \| Fair Value Hedging
Derivative Instruments and Hedging Activities Disclosures
Derivative, Notional Amount	$ 768.6	$ 736.4

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Nominal or face amount used to calculate payment on derivative.

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