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Derivative Financial Instruments Fair Value Hedges Carrying Amount of Hedged Assets and Liabilities and Cumulative Basis Adjustments (Details) - Interest Rate Swaps - Designated as Hedging Instrument - Fair Value Hedging - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
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Receive Variable/Pay Fixed | Fixed Maturity Securities |  |
Derivative Instruments and Hedging Activities Disclosures |  |
Hedged Asset, Fair Value Hedge | $ 48.1 | $ 48.5
Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease) | 0.1 | 0.6
Receive Fixed/Pay Fixed | Fixed Maturity Securities |  |
Derivative Instruments and Hedging Activities Disclosures |  |
Hedged Asset, Fair Value Hedge | 19.4 | 0.0
Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease) | (0.3) | 0.0
Receive Fixed/Pay Variable | Long-term Debt |  |
Derivative Instruments and Hedging Activities Disclosures |  |
Hedged Liability, Fair Value Hedge | (242.5) | (244.8)
Hedged Liability, Fair Value Hedge, Cumulative Increase (Decrease) | $ 6.9 | $ 4.5

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- Definition Amount of asset hedged in fair value hedging relationship. Type Reference Disclosure Reference Publisher FASB Name Accounting Standards Codification Topic 815 SubTopic 10 Section 50 Paragraph 4EE Subparagraph (a) URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109999712-113959 Change Note SourceName Hedging TaxonomyVersion 2018 ChangeDate 2017-11 NewElement true Source_ASU_Number 2017-12 + References No definition available. + Details
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- Definition Amount of cumulative increase (decrease) in fair value of hedged asset in fair value hedge, attributable to hedged risk. Disclosure Reference Publisher FASB Name Accounting Standards Codification Topic 815 SubTopic 10 Section 50 Paragraph 4EE Subparagraph (b) URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109999712-113959 Change Note SourceName Hedging TaxonomyVersion 2018 ChangeDate 2017-11 NewElement true Source_ASU_Number 2017-12 + References No definition available. + Details
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- Definition Amount of liability hedged in fair value hedging relationship. Disclosure Reference Publisher FASB Name Accounting Standards Codification Topic 815 SubTopic 10 Section 50 Paragraph 4EE Subparagraph (a) URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109999712-113959 Change Note SourceName Hedging TaxonomyVersion 2018 ChangeDate 2017-11 NewElement true Source_ASU_Number 2017-12 + References No definition available. + Details
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- Definition Amount of cumulative increase (decrease) in fair value of hedged liability in fair value hedge, attributable to hedged risk. Disclosure Reference Publisher FASB Name Accounting Standards Codification Topic 815 SubTopic 10 Section 50 Paragraph 4EE Subparagraph (b) URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109999712-113959 Change Note SourceName Hedging TaxonomyVersion 2018 ChangeDate 2017-11 NewElement true Source_ASU_Number 2017-12 + References No definition available. + Details
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