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Derivative Financial Instruments Fair Value Hedges Carrying Amount of Hedged Assets and Cumulative Basis Adjustments (Details) - Interest Rate Swaps - Receive Fixed/Pay Fixed - Designated as Hedging Instrument - Fair Value Hedging - USD ($) $ in Millions | Mar. 31, 2023 | Dec. 31, 2022
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Derivative Instruments and Hedging Activities Disclosures |  |
Hedged Asset, Statement of Financial Position [Extensible Enumeration] | Fixed Maturity Securities - at fair value (amortized cost of $38,101.8; $37,825.2; allowance for credit losses of $—; $—) | Fixed Maturity Securities - at fair value (amortized cost of $38,101.8; $37,825.2; allowance for credit losses of $—; $—)
Fixed Maturity Securities |  |
Derivative Instruments and Hedging Activities Disclosures |  |
Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease) | $ (21.6) | $ (24.8)

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