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Income Taxes - Components of net deferred tax assets (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Income taxes |  |
Balance carryforwards, gross value | $ 304.4 | $ 899.6
Deferred tax assets, future tax benefits | 303.9 | 430.4
Valuation allowance | (15.7) | (15.0)
Charitable contribution |  |
Income taxes |  |
Charitable contribution |  | 9.4
Deferred tax asset, charitable contribution |  | 4.0
Valuation allowance |  | (1.5)
Charitable contribution and capital loss |  |
Income taxes |  |
Charitable contributions and capital loss, gross value | 21.7 |
Deferred tax assets, charitable contributions and capital loss | 8.6 |
Valuation allowance | (2.1) |
Domestic tax authority |  |
Income taxes |  |
Tax credit carryforward, amount | 0.0 | 0.0
Operating loss carryforwards, gross value |  | 407.6
Deferred tax assets, operating loss carryforwards, domestic |  | 142.7
Deferred tax assets, tax credit carryforwards | 259.6 | 241.1
Tax credit carryforward, valuation allowance | (0.1) | 0.0
Operating loss carryforwards, valuation allowance |  | 0.0
Foreign tax authority |  |
Income taxes |  |
Tax credit carryforward, amount | 0.0 | 0.0
Deferred tax asset, federal foreign tax credit | 13.5 | 13.5
Tax credit carryforward, valuation allowance | (13.5) | (13.5)
State and local jurisdiction |  |
Income taxes |  |
Tax credit carryforward, amount | 0.0 | 0.0
Operating loss carryforwards, gross value | 282.7 | 482.6
Deferred tax assets, tax credit carryforwards | 5.0 | 4.8
Deferred tax asset, state net operating loss | 17.2 | 24.3
Tax credit carryforward, valuation allowance | 0.0 | 0.0
Operating loss carryforwards, valuation allowance | $ 0.0 | $ 0.0

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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible domestic operating loss carryforwards. Excludes state and local operating loss carryforwards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32621-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 20 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=96869850&loc=d3e28680-109314 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32632-109319 + Details
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