Investments (Net Realized Investment Gains/Losses And Net Change In Unrealized Appreciation/Depreciation In Investments) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investment [Line Items]
Gross realized gains from sales	$ 422.6	$ 374.3	$ 304.8
Gross realized losses from sales	(202.5)	(227.2)	(64.5)
Net realized gains on investments	220.1	147.1	240.3
Other-than-temporary impairment losses recognized in income	(115.4)	(83.4)	(49.0)
Total change in net unrealized gains (losses) on investments	197.7	(594.7)	181.7
Deferred income tax (expense) benefit	(79.8)	210.4	(63.1)
Net change in net unrealized gains (losses) on investments	117.9	(384.3)	118.6
Net realized gains (losses) on investments, other-than-temporary impairment losses recognized in income and net change in net unrealized gains (losses) on investments	222.6	(320.6)	309.9
Fixed Maturity Securities [Member]
Investment [Line Items]
Gross realized gains from sales	209.9	135.9	198.2
Gross realized losses from sales	(152.1)	(182.1)	(50.6)
Net realized gains (losses) from sales	57.8	(46.2)	147.6
Other-than-temporary impairment losses recognized in income	(74.7)	(31.2)	(22.3)
Total change in net unrealized gains (losses) on investments	193.3	(372.9)	145.2
Equity Securities [Member]
Investment [Line Items]
Gross realized gains from sales	205.5	233.4	93.5
Gross realized losses from sales	(50.0)	(45.1)	(13.9)
Net realized gains (losses) from sales	155.5	188.3	79.6
Other-than-temporary impairment losses recognized in income	(22.3)	(35.6)	(13.5)
Total change in net unrealized gains (losses) on investments	6.9	(217.7)	36.5
Other Investments [Member]
Investment [Line Items]
Gross realized gains from sales	7.2	5.0	13.1
Gross realized losses from sales	(0.4)	0.0	0.0
Net realized gains from sales of other investments	6.8	5.0	13.1
Other-than-temporary impairment losses recognized in income	(18.4)	(16.6)	(13.2)
Total change in net unrealized gains (losses) on investments	$ (2.5)	$ (4.1)	$ 0.0

Deferred income tax expense benefit related to unrealized gain loss on investments.

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- Definition

Gross Realized Gains From Sale of Other Investments

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Gross Realized Losses From Sale of Other Investments

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- Definition

Net Realized Gains Losses On Investments Other Than Temporary Impairment Losses Recognized In Income And Net Change In Net Unrealized Gains Losses On Investments

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No definition available.

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- Definition

Line items represent reporting 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 12
-Sentence Column A

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This item represents the pretax change in net unrealized holding gain (loss) on available-for-sale securities that has been included in accumulated other comprehensive income, a separate component of shareholders' equity, during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

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The change in unrealized holding gain (loss), net of tax, on available-for-sale securities included in a separate component of shareholders' equity during the period.

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- Definition

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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-Paragraph 9
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- Definition

The difference between the book value and the sale price of other nonspecific investments. This element is used when other, more specific, elements are not appropriate. This element refers to the gain (loss) included in earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
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- Definition

The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 8B
-URI http://asc.fasb.org/extlink&oid=27724398&loc=SL6284393-111563

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The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.3(a))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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