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Summary of Significant Accounting Policies - Changes in the Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Pre-tax | $ (31.3) | $ 52.0 | $ 9.7
Tax | (3.8) | (2.1) | (7.6)
Net of Tax | 30.2 | (49.9) | (2.1)
Net of Tax | (35.1) |  |
Pension and OPEB liability adjustments |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Pre-tax | (0.9) | 15.4 | 3.4
Tax | (2.4) | (3.8) | (4.3)
Net of Tax | 3.3 | (11.6) | 0.9
Derivative instrument adjustments |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Pre-tax | (2.4) |  |
Tax | 1.4 |  |
Net of Tax | 1.0 |  |
Derivative instrument adjustments |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Pre-tax |  | 5.1 | 23.0
Tax |  | (2.8) | (3.3)
Net of Tax |  | (2.3) | (19.7)
Unrealized foreign currency translation adjustments |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Pre-tax | (28.0) | 31.5 | (16.7)
Tax | (2.8) | 4.5 | 0.0
Net of Tax | 30.8 | $ (36.0) | $ 16.7
Accounting Standards Update 2018-02 [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets | $ 4.9 |  |

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