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Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2017
Accounting Policies [Abstract] |
Summary of Deferred Policy Acquisition Cost Amortization and Net Advertising Expense [Table Text Block] | The table below presents a summary of deferred policy acquisition cost amortization and net advertising expense:
| Year Ended December 31,
| 2017 |  | 2016 |  | 2015
| (Amounts in millions)
Deferred policy acquisition cost amortization | $ | 555.4 |  |  | $ | 562.5 |  |  | $ | 539.2 |
Net advertising expense | 37.4 |  |  | 39.6 |  |  | 44.0 |

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