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Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions |  | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Jan. 01, 2019 | Sep. 30, 2019 | Mar. 31, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |
Other comprehensive loss before income tax effect |  | $ (102.0) |  |  | $ (102.0) |  | $ (104.8)
Income tax effect |  | 4.0 |  |  | 4.0 |  | 6.1
Accumulated other comprehensive loss |  | (98.0) |  |  | (98.0) |  | (98.7)
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |  |  |
Balance, start | $ 762.2 | 709.4 | $ 762.2 | $ 853.1 | 762.2 | $ 829.6 |
Impact of ASU 2018-02 |  |  | 1.3 |  |  |  |
Balance, end |  | 689.9 |  | 833.5 | 689.9 | 833.5 |
Defined benefit plan and other postretirement liabilities [Member] |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |
Other comprehensive loss before income tax effect |  | (104.3) |  |  | (104.3) |  | (107.3)
Income tax effect |  | (4.5) |  |  | (4.5) |  | (6.6)
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |  |  |
Balance, start | (100.7) | (100.7) | (100.7) | (90.8) | (100.7) | (93.8) |
Impact of ASU 2018-02 | (1.3) |  |  |  |  |  |
Net amount reclassified to net income (loss) |  | 0.7 |  | 0.1 | 2.1 | 3.2 |
Balance, end |  | (100.0) |  | (90.7) | (100.0) | (90.7) |
Unrealized gain (loss) on financial instruments [Member] |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |
Other comprehensive loss before income tax effect |  | 2.3 |  |  | 2.3 |  | 2.5
Income tax effect |  | 0.5 |  |  | 0.5 |  | $ 0.5
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |  |  |
Balance, start | 2.0 | 2.0 | 2.0 | 2.1 | 2.0 | 2.1 |
Impact of ASU 2018-02 | 0.0 |  |  |  |  |  |
Net amount reclassified to net income (loss) |  | (0.0) |  | (0.0) | (0.1) | (0.1) |
Balance, end |  | 2.0 |  | 2.1 | 2.0 | 2.1 |
Accumulated other comprehensive loss [Member] |  |  |  |  |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |  |  |  |  |
Balance, start | (98.7) | (98.7) | $ (98.7) | (88.7) | (98.7) | (91.7) |
Impact of ASU 2018-02 | $ (1.3) |  |  |  |  |  |
Net amount reclassified to net income (loss) |  | 0.7 |  | 0.1 | 2.0 | 3.1 |
Balance, end |  | $ (98.0) |  | $ (88.7) | $ (98.0) | $ (88.7) |

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