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Income Tax Expense - NOL and Tax Credit Carryforwards (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
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Federal [Member] |  |  |
NOL and Tax Credit Carryforwards [Line Items] |  |  |
NOL Carryforwards | [1] | $ 177.3 | $ 197.5
Tax Credit Carryforwards |  | 416.4 | 362.9
Tax Credit Carryforwards, Valuation Allowance |  | 0.0 |
NOL Carryforwards, Valuation Allowance |  | 0.0 |
State [Member] |  |  |
NOL and Tax Credit Carryforwards [Line Items] |  |  |
NOL Carryforwards | [1] | 506.9 | 270.1
Tax Credit Carryforwards | [2] | 24.2 | 23.4
Tax Credit Carryforwards, Valuation Allowance |  | $ 68.6 | $ 69.4
[1] | Pre-tax amounts.
[2] | Net of a $68.6 million valuation allowance as of December 31, 2021 ($69.4 million as of December 31, 2020).

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- Definition NOL and Tax Credit Carryforwards [Line Items] + References No definition available. + Details
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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32559-109319 + Details
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- Definition The portion of the valuation allowance pertaining to the deferred tax asset representing potential future taxable deductions from net operating loss carryforwards for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319 + Details
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- Definition The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32559-109319 + Details
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- Definition Amount of valuation allowance pertaining to the deferred tax asset representing potential future taxable deductions from tax credit carryforwards for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319 + Details
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