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SCHEDULE I SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES (Details) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | --- | ---
Summary of investments other than investments in related parties |  |  |
Fixed maturity investments, at fair value | $ 4,250.2 | $ 2,630.2 |
Cost | 5,308.8 |  |
Carrying Value | 5,341.5 |  |
Fair Value | 5,341.5 |  |
Fair value investments | 5,039.7 | 4,050.9 | $ 3,343.6
Fixed maturity investments |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 4,266.0 |  |
Carrying Value | 4,256.8 |  |
Fair Value | 4,256.8 |  |
US Government and agency obligations |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 281.7 |  |
Carrying Value | 278.3 |  |
Fair Value | 278.3 |  |
Debt securities issued by corporations |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 1,512.6 |  |
Carrying Value | 1,509.4 |  |
Fair Value | 1,509.4 |  |
Municipal obligations |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 308.8 |  |
Carrying Value | 309.0 |  |
Fair Value | 309.0 |  |
Mortgage and asset-backed securities |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 2,141.7 |  |
Carrying Value | 2,132.9 |  |
Fair Value | 2,132.9 |  |
Foreign government, agency and provincial obligations |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 12.9 |  |
Carrying Value | 13.2 |  |
Fair Value | 13.2 |  |
Preferred stocks |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 8.3 |  |
Carrying Value | 14.0 |  |
Fair Value | 14.0 |  |
Short-term investments |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 287.1 |  |
Carrying Value | 287.1 |  |
Fair Value | 287.1 |  |
Exchange Traded Funds [Member] |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 316.4 |  |
Carrying Value | 321.6 |  |
Fair Value | 321.6 |  |
Common equity securities |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 440.8 |  |
Carrying Value | 474.3 |  |
Fair Value | 474.3 |  |
Banks, trust and insurance companies |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 11.2 |  |
Carrying Value | 11.6 |  |
Fair Value | 11.6 |  |
Public utilities |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 0.0 |  |
Carrying Value | 0.0 |  |
Fair Value | 0.0 |  |
Industrial, miscellaneous and other |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 113.2 |  |
Carrying Value | 141.1 |  |
Fair Value | 141.1 |  |
Other long-term investments |  |  |
Summary of investments other than investments in related parties |  |  |
Cost | 314.9 |  |
Carrying Value | 323.3 |  |
Fair Value | 323.3 |  |
Fair value measured on a recurring basis |  |  |
Summary of investments other than investments in related parties |  |  |
Fair value investments | 5,195.9 | 4,134.4 |
Fair value measured on a recurring basis | Other long-term investments |  |  |
Summary of investments other than investments in related parties |  |  |
Fair value investments | 177.7 | 169.5 |
Level 3 | Other long-term investments |  |  |
Summary of investments other than investments in related parties |  |  |
Fair value investments | 177.7 | 169.5 | 125.9
Level 3 | Fair value measured on a recurring basis |  |  |
Summary of investments other than investments in related parties |  |  |
Fair value investments | 177.7 | 239.5 |
Level 3 | Fair value measured on a recurring basis | Forward Contracts [Member] |  |  |
Summary of investments other than investments in related parties |  |  |
Fair value investments | (1.2) |  |
Level 3 | Fair value measured on a recurring basis | Other long-term investments |  |  |
Summary of investments other than investments in related parties |  |  |
Carrying value of investment accounted for using the equity method | 3.5 | 3.8 | 5.2
Fair value investments | 177.7 | 169.5 |
Affordable Housing Development Fund [Member] | Other long-term investments |  |  |
Summary of investments other than investments in related parties |  |  |
Fair value investments | 12.3 | 14.7 | 16.8
Star & Shield Insurance Exchange [Member] | Fixed maturity investments |  |  |
Summary of investments other than investments in related parties |  |  |
Fixed maturity investments, at fair value | 6.6 | 9.5 | $ 10.1
Star & Shield Insurance Exchange [Member] | Short-term investments |  |  |
Summary of investments other than investments in related parties |  |  |
Fixed maturity investments, at fair value | $ 0.1 | $ 0.1 |

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