Investments Federal Home Loan Bank Carrying Value of Common Stock, Collateral Posted and Advances Received (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Schedule of Federal Home Loan Bank Information
Federal Home Loan Bank Stock	$ 34.1	$ 34.1
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	350.0	350.0
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	590.1	544.8
Fixed Maturity Securities
Schedule of Federal Home Loan Bank Information
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	268.5	213.3
Mortgage Loans as Collateral
Schedule of Federal Home Loan Bank Information
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	$ 321.6	$ 331.5

Schedule of Federal Home Loan Bank Information [Line Items]

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- Definition

Amount of advances from the Federal Home Loan Bank (FHLB).

+ References

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- Definition

Amount of the collateral pledged in support of federal home loan bank advances outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

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- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 325
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75031641&loc=d3e63345-112809

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