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Income Taxes, Tax Act (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Income Taxes [Abstract] |  |  |
U.S. federal corporate tax rate | 21.00% | 35.00% | 35.00%
Provisional tax expense for impact of change in tax rate on deferred tax assets under the Tax Act |  | $ 107.3 |

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