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Components of accumulated other comprehensive loss (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Other comprehensive loss before income tax effect | $ (98.6) |  | $ (99.4)
Income tax effect | 7.3 |  | 7.7
Accumulated other comprehensive loss | (91.3) |  | (91.7)
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Equity, beginning balance | 829.6 |  |
Equity, ending balance | 830.4 |  |
Defined benefit plan and other postretirement liabilities [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Other comprehensive loss before income tax effect | (101.2) |  | (102.1)
Income tax effect | 7.8 |  | 8.2
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Equity, beginning balance | (93.8) | $ (116.2) |
Net amount reclassified to net loss | 0.4 | 0.7 |
Equity, ending balance | (93.4) | (115.5) |
Unrealized gain (loss) on financial instruments [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Other comprehensive loss before income tax effect | 2.6 |  | 2.7
Income tax effect | (0.5) |  | $ (0.5)
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Equity, beginning balance | 2.1 | 2.3 |
Net amount reclassified to net loss | 0.0 | 0.0 |
Equity, ending balance | 2.1 | 2.3 |
AOCI Attributable to Parent [Member] |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Equity, beginning balance | (91.7) | (113.9) |
Net amount reclassified to net loss | 0.4 | 0.7 |
Equity, ending balance | $ (91.3) | $ (113.2) |

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- Definition Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e681-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580 + Details
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