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Income Taxes (Net Operating and Capital Loss Carryforwards) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Net deferred tax assets |  |  |
Total net deferred income tax assets | $ 215.8 | $ 218.3 |
Change in valuation allowance | (9.1) | 19.4 | $ 35.7
Alternative minimum tax credit carryforwards, not subject to expiration | 2.3 |  |
Tax credit carryforwards | 20.7 | 16.9 |
UNITED STATES |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | (4.2) |  |
Net deferred tax assets |  |  |
Foreign tax credit carryforwards, subject to expiration | 0.4 |  |
Tax credit carryforwards | 18.0 |  |
Operating and Capital Loss Carryforward |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 675.5 |  |
Net deferred tax assets |  |  |
Gross deferred tax asset | 218.8 |  |
Valuation allowance | (144.9) |  |
Total net deferred income tax assets | 73.9 |  |
Operating and Capital Loss Carryforward | UNITED STATES |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 558.7 |  |
Net deferred tax assets |  |  |
Gross deferred tax asset | 189.3 |  |
Valuation allowance | (115.4) |  |
Total net deferred income tax assets | 73.9 |  |
Operating and Capital Loss Carryforward | Luxembourg |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 93.8 |  |
Net deferred tax assets |  |  |
Gross deferred tax asset | 24.4 |  |
Valuation allowance | (24.4) |  |
Total net deferred income tax assets | 0.0 |  |
Operating and Capital Loss Carryforward | Foreign Tax Authority [Member] |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 19.8 |  |
Net deferred tax assets |  |  |
Gross deferred tax asset | 4.6 |  |
Valuation allowance | (4.6) |  |
Total net deferred income tax assets | 0.0 |  |
Operating and Capital Loss Carryforward | UNITED KINGDOM |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 3.2 |  |
Net deferred tax assets |  |  |
Gross deferred tax asset | 0.5 |  |
Valuation allowance | (0.5) |  |
Total net deferred income tax assets | 0.0 |  |
No expiration date [Member] | Operating and Capital Loss Carryforward |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 116.8 |  |
No expiration date [Member] | Operating and Capital Loss Carryforward | UNITED STATES |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 0.0 |  |
No expiration date [Member] | Operating and Capital Loss Carryforward | Luxembourg |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 93.8 |  |
No expiration date [Member] | Operating and Capital Loss Carryforward | Foreign Tax Authority [Member] |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 19.8 |  |
No expiration date [Member] | Operating and Capital Loss Carryforward | UNITED KINGDOM |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 3.2 |  |
2027-2036 | Operating and Capital Loss Carryforward |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 556.3 |  |
2027-2036 | Operating and Capital Loss Carryforward | UNITED STATES |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 556.3 |  |
2027-2036 | Operating and Capital Loss Carryforward | Luxembourg |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 0.0 |  |
2027-2036 | Operating and Capital Loss Carryforward | Foreign Tax Authority [Member] |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 0.0 |  |
2024-2033 [Member] | Operating and Capital Loss Carryforward | UNITED KINGDOM |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 0.0 |  |
2022-2026 | Operating and Capital Loss Carryforward |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 1.6 |  |
2022-2026 | Operating and Capital Loss Carryforward | UNITED STATES |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 1.6 |  |
2022-2026 | Operating and Capital Loss Carryforward | Luxembourg |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 0.0 |  |
2022-2026 | Operating and Capital Loss Carryforward | Foreign Tax Authority [Member] |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 0.0 |  |
2019-2013 [Member] | Operating and Capital Loss Carryforward | UNITED KINGDOM |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 0.0 |  |
2017-2021 | Operating and Capital Loss Carryforward |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 0.8 |  |
2017-2021 | Operating and Capital Loss Carryforward | UNITED STATES |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 0.8 |  |
2017-2021 | Operating and Capital Loss Carryforward | Luxembourg |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 0.0 |  |
2017-2021 | Operating and Capital Loss Carryforward | Foreign Tax Authority [Member] |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 0.0 |  |
2014-2018 [Member] | Operating and Capital Loss Carryforward | UNITED KINGDOM |  |  |
Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon |  |  |
Operating Loss Carryforwards | 0.0 |  |
Star & Shield Insurance Exchange [Member] |  |  |
Net deferred tax assets |  |  |
Change in valuation allowance | $ (6.9) | $ 1.2 |

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