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Financing Obligations (Senior Secured Notes) (Details) - USD ($) $ in Millions |  |  | 12 Months Ended
--- | --- | --- | ---
Apr. 03, 2017 | Mar. 27, 2014 | Dec. 31, 2017 | Dec. 31, 2016
Debt and Financing Obligations [Line Items] |  |  |  |
Borrowings |  |  | $ 7.5 | $ 304.9
Payments for redemption of senior secured notes |  |  | 327.2 | 0.0
Interest expense on debt instruments issued |  |  | 12.2 | 24.4
Senior Secured Notes [Member] |  |  |  |
Debt and Financing Obligations [Line Items] |  |  |  |
Borrowings |  |  | $ 0.0 | $ 297.6
Offering price as percent of par |  | 96.524% |  |
Proceeds from issuance of secured debt |  | $ 304.1 |  |
Redemption price as percent of par | 103.875% |  |  |
Payments for redemption of senior secured notes | $ 327.2 |  |  |
Interest expense on debt instruments issued | 12.2 |  |  |
Pre-tax loss related to redemption of debt instruments | 29.1 |  |  |
Deferred tax assets, redemption of debt instruments | $ 7.3 |  |  |
Gross carrying amount [member] | Senior Secured Notes [Member] |  |  |  |
Debt and Financing Obligations [Line Items] |  |  |  |
Borrowings |  | $ 315.0 |  |

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