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Investments - Distribution of Fixed Maturity Securities by Expected Maturity (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2021 | Dec. 31, 2020
Percent of Total Fair Value |  |
Due in 1 year or less | 4.10% | 4.00%
Due after 1 year through 5 years | 28.20% | 28.30%
Due after 5 years through 10 years | 28.30% | 28.00%
Due after 10 years through 20 years | 24.00% | 24.60%
Due after 20 years | 15.40% | 15.10%
Total | 100.00% | 100.00%
Fair Value |  |
Due in 1 year or less | $ 261.3 |
Due after 1 year through 5 years | 1,789.8 |
Due after 5 years through 10 years | 1,799.7 |
Due after 10 years through 20 years | 1,523.5 |
Due after 20 years | 982.0 |
Total | 6,356.3 | $ 6,345.3
Amortized Cost, net |  |
Due in 1 year or less | 255.5 |
Due after 1 year through 5 years | 1,713.5 |
Due after 5 years through 10 years | 1,669.5 |
Due after 10 years through 20 years | 1,412.2 |
Due after 20 years | 942.0 |
Amortized Cost, net | $ 5,992.7 | $ 5,788.6
Average option-adjusted duration, in years | 6 years 7 months 6 days | 6 years 4 months 24 days

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