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Quantitative Information Regarding Significant Unobservable Inputs (Details) - Fair Value, Inputs, Level 3 - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 | Dec. 31, 2017
Embedded Derivative Liability |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs |  | $ (17.6) | $ (15.9)
Embedded Derivative Liability | Projected Cash Flows |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |
Significant Assumptions to Calculating Fair Value of Level 3 Instrument | [1] | Actuarial Assumptions | Actuarial Assumptions
All Other Corporate Bonds - Private |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs |  | $ 276.6 | $ 244.4
All Other Corporate Bonds - Private | Market Convention |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |
Significant Assumptions to Calculating Fair Value of Level 3 Instrument | [2] | Priced at Par | Priced at Par
All Other Corporate Bonds - Private | Minimum |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |
Comparability Adjustments | [3] | 1.00% | 0.20%
Lack of Marketability | [4] | 0.25% | 0.25%
Volatility of Credit | [5] | 0.20% | 0.12%
All Other Corporate Bonds - Private | Maximum |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |
Comparability Adjustments | [3] | 1.25% | 0.20%
Lack of Marketability | [4] | 0.25% | 0.25%
Volatility of Credit | [5] | 5.82% | 6.25%
All Other Corporate Bonds - Private | Weighted Average |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |
Comparability Adjustments | [3] | 1.04% | 0.20%
Lack of Marketability | [4] | 0.25% | 0.25%
Volatility of Credit | [5] | 0.59% | 0.50%
Equity Securities |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs |  | $ 1.1 | $ 1.1
Equity Securities | Market Convention |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |
Significant Assumptions to Calculating Fair Value of Level 3 Instrument | [2] | Priced at Cost or Owner's Equity | Priced at Cost or Owner's Equity
[1] | Represents various actuarial assumptions required to derive the liability cash flows including incidence, termination, and lapse rates
[2] | Represents a decision to price based on par value, cost, or owner's equity when limited data is available
[3] | Represents basis point adjustments for changes in benchmark spreads associated with various industry sectors
[4] | Represents basis point adjustments to apply a discount due to the illiquidity of an investment
[5] | Represents basis point adjustments for credit-specific factors

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- Definition Percentage of adjustment to the observed price for a similar asset or liability when an identical transaction does not exist, used as an input to measure fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Adjustment to the discount rate used to measure fair value for lack of ability to convert business interests into cash quickly. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Risk associated with risk of default, credit spread risk and downgrade risk, expressed as a percentage, used as an input to measure fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Description of significant assumptions used by management to measure fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611 + Details
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