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Summary of Significant Accounting Policies Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Accumulated other comprehensive (income) loss |  | $ (32.1) | $ (27.9) | $ (28.9)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax |  | (8.2) | (9.1) |
Amounts reclassified from accumulated other comprehensive income (loss) |  | (3.9) | (3.4) | (3.3)
Amounts reclassified from accumulated other comprehensive income (loss) |  | 2.1 | 1.5 |
Amounts Reclassified from Accumulated OCI, Net of Tax and Noncontrolling Interest |  | 4.0 | 10.1 |
Other Comprehensive Income (Loss), Net of Tax |  | (4.2) | 1.0 | (5.7)
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax |  | 2.2 | 8.6 | 4.7
Pension Plans, Defined Benefit [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Amounts reclassified from accumulated other comprehensive income (loss) |  | (6.1) | (12.0) |
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax | [1] | (5.1) | (4.5) |
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax | [1] | (2.9) | (11.3) |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax |  | (8.0) | (15.8) |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax |  | (1.9) | (3.8) |
Other Postretirement Benefits Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Amounts reclassified from accumulated other comprehensive income (loss) |  | 2.1 | 1.9 |
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax | [1] | 0.1 | 0.2 |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax | [1] | 2.3 | 2.3 |
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax | [1] | 0.4 | 0.0 |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax |  | 2.8 | 2.5 |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax |  | 0.7 | 0.6 |
Defined Benefit Plans Income Loss [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Accumulated other comprehensive income (loss) |  | (34.1) | (35.1) | (38.8)
Other comprehensive income before reclassifications |  | (5.1) |  |
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax |  |  | (8.3) |
Amounts reclassified from accumulated other comprehensive income (loss) |  | 3.9 | 3.4 |
Other Comprehensive Income (Loss), Net of Tax |  | 1.0 | 3.7 |
Defined Benefit Plans Income Loss [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Accumulated other comprehensive income (loss) |  | 1.4 | 4.2 | 4.6
Other comprehensive income before reclassifications |  | (2.4) |  |
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax |  |  | (0.2) |
Amounts reclassified from accumulated other comprehensive income (loss) |  | (0.1) | (0.2) |
Other Comprehensive Income (Loss), Net of Tax |  | (2.8) | (0.4) |
AOCI Attributable to Parent [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Net of Tax |  | (4.2) | 1.0 | (5.7)
Defined Benefit Plan Prior Service Cost [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Accumulated other comprehensive income (loss) |  | 1.9 | 3.6 | 5.3
Other comprehensive income before reclassifications |  | 0.0 |  |
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax |  |  | 0.0 |
Amounts reclassified from accumulated other comprehensive income (loss) |  | (1.7) | (1.7) |
Other Comprehensive Income (Loss), Net of Tax |  | (1.7) | (1.7) |
Settlement Cost [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax |  | 2.2 | 8.6 |
Settlement Cost [Member] | Defined Benefit Plans Income Loss [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax |  | 0.0 | 0.0 |
Settlement Cost [Member] | Defined Benefit Plan Prior Service Cost [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax |  | 2.2 | 8.6 |
Settlement Cost [Member] | Defined Benefit Plan Prior Service Cost [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax |  | 0.0 | 0.0 |
Curtailment |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax |  | (0.3) |  |
Curtailment | Defined Benefit Plans Income Loss [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax |  | 0.0 |  |
Curtailment | Defined Benefit Plans Income Loss [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax |  | (0.3) |  |
Curtailment | Defined Benefit Plan Prior Service Cost [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax |  | 0.0 |  |
Commodity Contract [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
OCI, before Reclassifications, Net of Tax, Attributable to Parent |  |  | (0.6) |
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax |  | (0.7) |  |
Amounts reclassified from accumulated other comprehensive income (loss) |  | 0.0 | 0.0 |
Net current period other comprehensive income (loss) |  | (0.7) | (0.6) |
AOCI, Derivative Qualifying as Hedge, Excluded Component, after Tax |  | (1.3) | (0.6) | $ 0.0
Commodity Contract [Member] | Settlement Cost [Member] |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax |  | 0.0 | $ 0.0 |
Commodity Contract [Member] | Curtailment |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax |  | $ 0.0 |  |
[1] | These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost (see Note 13 for additional information).

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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/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(30)(a)(4)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e637-108580 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(23)(a)(3)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (h)(2) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (g)(2)(ii) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e681-108580 + Details
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