Fair Value Disclosures (Carrying Value And Fair Value Of The Financial Instruments That Are Not Recognized Or Are Not Carried At Fair Value) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Funds withheld under reinsurance	$ 179.8	$ 111.7
Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial mortgage loans on real estate	679.2	634.9
Other investments	84.4	74.8
Total financial assets	763.6	709.7
Individual and group annuities, subject to discretionary withdrawal	642.5	680.4
Funds withheld under reinsurance	179.8	111.7
Debt	1,174.4	1,159.7
Total financial liabilities	1,996.7	1,951.8
Level 1 \| Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial mortgage loans on real estate	0.0	0.0
Other investments	36.3	38.5
Total financial assets	36.3	38.5
Individual and group annuities, subject to discretionary withdrawal	0.0	0.0
Funds withheld under reinsurance	179.8	111.7
Debt	0.0	0.0
Total financial liabilities	179.8	111.7
Level 2 \| Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial mortgage loans on real estate	0.0	0.0
Other investments	0.0	0.0
Total financial assets	0.0	0.0
Individual and group annuities, subject to discretionary withdrawal	0.0	0.0
Funds withheld under reinsurance	0.0	0.0
Debt	1,174.4	1,159.7
Total financial liabilities	1,174.4	1,159.7
Level 3 \| Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial mortgage loans on real estate	679.2	634.9
Other investments	48.1	36.3
Total financial assets	727.3	671.2
Individual and group annuities, subject to discretionary withdrawal	642.5	680.4
Funds withheld under reinsurance	0.0	0.0
Debt	0.0	0.0
Total financial liabilities	642.5	680.4
Carrying Value \| Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial mortgage loans on real estate	670.2	624.0
Other investments	84.4	74.8
Total financial assets	754.6	698.8
Individual and group annuities, subject to discretionary withdrawal	634.3	651.0
Funds withheld under reinsurance	179.8	111.7
Debt	1,068.2	1,067.0
Total financial liabilities	$ 1,882.3	$ 1,829.7

Policy Reserves Under Investment Products, Fair Value Disclosure

No definition available.

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- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ References

No definition available.

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of funds held as security for payments to be received under reinsurance contracts.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.13(c))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Glossary Available-for-Sale Securities
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+ Details

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- Definition

Aggregation of the liabilities reported on the balance sheet measured at fair value on a nonrecurring basis by the entity.

+ References

No definition available.

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- Definition

Fair value portion of mortgage loans held-for-sale.

+ References

No definition available.

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