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Fair Value Measurements (Tables) | 12 Months Ended
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Dec. 31, 2017
Fair Value Disclosures [Abstract] |
Fair Value of Debt |
| December 31, 2017 |  | December 31, 2016
| Nominal Unpaid Principal Balance |  | Aggregate Fair Value |  | Nominal Unpaid Principal Balance |  | Aggregate Fair Value
Debt | $ | 2,174.3 |  |  | $ | 2,260.9 |  |  | $ | 2,215.3 |  |  | $ | 2,275.5 |

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- Definition Tabular disclosure of information pertaining to carrying amount and estimated fair value of short-term and long-term debt instruments or arrangements, including but not limited to, identification of terms, features, and collateral requirements. + References No definition available. + Details
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