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Investments Distribution of the Maturity Dates for Fixed Maturity Securities (Details) - USD ($) $ in Millions | Jun. 30, 2023 | Dec. 31, 2022
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Debt Securities, Available-for-sale, Amortized Cost, Net of Allowance for Credit Losses, Fiscal Year Maturity |  |
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One, Net | $ 902.9 | $ 1,133.5
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five, Net | 7,787.1 | 7,090.8
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10, Net | 9,706.2 | 10,096.7
Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10, Net | 19,055.2 | 18,912.1
Available for sale Securities Debt Maturities Amortized Cost Gross Subtotal, Net | 37,451.4 | 37,233.1
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost, Net | 576.7 | 592.1
Debt Securities, Available-for-sale, Amortized Cost, Net of Allowance for Credit Losses | 38,028.1 | 37,825.2
Available for Sale Securities Unrealized Gain Position Gross Gain |  |
Available For Sale Securities Debt Maturities Within One Year Unrealized Gain Position Gross Gain | 1.6 | 2.9
Available For Sale Securities Debt Maturities After One Through Five Years Unrealized Gain Position Gross Gain | 73.0 | 86.7
Available For Sale Securities Debt Maturities After Five Through Ten Years Unrealized Gain Position Gross Gain | 298.5 | 294.8
Available For Sale Securities Debt Maturities After Ten Years Unrealized Gain Position Gross Gain | 431.1 | 351.0
Available For Sale Securities Debt Maturities Unrealized Gain Position Gross Gain Gross Subtotal | 804.2 | 735.4
Available For Sale Securities Debt Maturities Without Single Maturity Date Unrealized Gain Position Gross Gain | 6.4 | 8.2
Available for sale Securities, Debt Maturities Unrealized Gain Position Gross Gain | 810.6 | 743.6
Available for Sale Securities Unrealized Loss Position Gross Loss |  |
Available For Sale Securities Debt Maturities Within One Year Unrealized Loss Position Gross Loss | 5.8 | 5.7
Available For Sale Securities Debt Maturities After One Through Five Years Unrealized Loss Position Gross Loss | 297.9 | 238.4
Available For Sale Securities Debt Maturities After Five Through Ten Years Unrealized Loss Position Gross Loss | 811.9 | 863.8
Available For Sale Securities Debt Maturities After Ten Years Unrealized Loss Position Gross Loss | 2,322.0 | 2,593.1
Available For Sale Securities Debt Maturities Unrealized Gain Position Gross Loss Gross Subtotal | 3,437.6 | 3,701.0
Available For Sale Securities Debt Maturities Without Single Maturity Date Unrealized Loss Position Gross Loss | 27.0 | 27.0
Available For Sale Securities Unrealized Loss Position Gross Loss Subtotal | 3,464.6 | 3,728.0
Fair Value Maturity Distribution |  |
Debt Securities, Available-for-sale, Total | 35,374.1 | 34,840.8
Available for Sale Securities Unrealized Gain Position Fair Value |  |
Fair Value Maturity Distribution |  |
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value | 227.4 | 339.1
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Fair Value | 1,839.3 | 1,953.2
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value | 3,490.9 | 3,538.9
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value | 5,905.7 | 5,013.2
Available for sale Securities Debt Maturities Fair Value Gross Subtotal | 11,463.3 | 10,844.4
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value | 165.6 | 186.6
Debt Securities, Available-for-sale, Total | 11,628.9 | 11,031.0
Available for Sale Securities Unrealized Loss Position Fair Value |  |
Fair Value Maturity Distribution |  |
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value | 671.3 | 791.6
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Fair Value | 5,722.9 | 4,985.9
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value | 5,701.9 | 5,988.8
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value | 11,258.6 | 11,656.8
Available for sale Securities Debt Maturities Fair Value Gross Subtotal | 23,354.7 | 23,423.1
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value | 390.5 | 386.7
Debt Securities, Available-for-sale, Total | $ 23,745.2 | $ 23,809.8

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